Challenges in Grease Selection Without Full Bearing Specifications

Bearing manufacturers have provided a significant amount of detailed advice for lubricant selection, application, and replenishment.  Formulas used by the machine designers incorporate details that are typically not readily available to the maintenance practitioner, namely load rating and ratio, grease L₁₀ lifecycle, and specific bearing dimensions. 

 The bearing diameters (OD, ID) may be satisfactorily estimated, but there are multiple bearing models for a bearing type that will share a bore dimension.  Without the correct bore and outer diameter, it is impossible to arrive at an exact replacement volume.

The Role of Grease Viability in Replacement Frequency

 Grease viability drives replacement frequency. Grease Viability is best determined by testing.  Per DIN 51825, greases can be evaluated under laboratory conditions to deliver a provisional expected lifecycle, with results reported in either L₁₀ or L₅₀ values. The grease’s L₁₀ and L₅₀ values depict operating hours to 90% and 50% viability. The frictional measurement of a loaded bearing in the FE8 test stand determines grease viability. 

Without grease viability data, replacement frequency is always an educated guess.

 When the grease can no longer separate and protect surfaces during test conditions, it is evidenced by an increase in friction beyond a threshold. At this point, the test hours are noted, and the grease is assigned a value in hours for grease viability. These values are not often published for customer use. Without these discrete pieces of information for the greased bearing, estimating the best replacement frequency is challenging.

Engineering Principles for Reliability-Centric Grease Relubrication

Suppose the machine owner wants to use machine lubrication as a leading practice to improve machine reliability. In that case, the machine owner must invest time to fully define the bearing and lubricant details to calculate appropriate volumes and intervals to deliver reliability-centric lubrication practices.

 This article presents the engineering principles for bearing grease relubrication, including consideration for open, single, and double shielded bearing configurations, and will include both theoretical methods and general advice useful to calculate both volumes and intervals when the exact details are not available.   The calculations presented here are also used to define volume and frequency for operating conditions.

Even without full specs, sound engineering principles can guide precise grease relubrication.

 Bearing manufacturers have provided detailed advice for selecting lubricant type, volume, and frequency requirements. They intend to assist the user with placing the optimum volume of a lubricant product with viscometric properties and surface performance (AW and EP) additives that precisely address the operating parameters (heat, load, vibration, moisture, contaminant, process chemical challenges).

Once accomplished, the user can expect the grease to feed oil to the race incrementally between the current date and the planned replenishment date so that the replacement practice provides a seamless flow of lubricant to the load zone, as depicted in Figure 1.

Either too much or too little grease, and/or inappropriately high or low oil viscosity causes viscous drag and/or destruction of the bearing surfaces and lubricant within the bearing. 

In moderate and high-speed bearings (nDm > 150K), even slight variations in consistency of replenishment and fill volume produce effects including dry surfaces and elevated high-frequency vibration (inadequate feed), elevated temperatures and increased energy consumption (overfeed).

The faster the shaft speed, and the higher the load, the more pronounced the deficiencies. As the shaft speed decreases, the negative impact (churning, overheating, and energy losses) declines, but is still evident. The first part of this multi-part document addresses lubricant viscosity and NLGI selection. 

The second part addresses volume and frequency. The third part addresses sealed and shielded bearings and electric motor configurations.

Lubricant Selection: Viscosity, Additives, and NLGI Grade

Understanding the Impact of Viscosity on Bearing Performance

Viscosity changes with temperature and pressure. As temperature increases, viscosity decreases, and as pressure increases, viscosity increases. These factors are interdependent on one another. The central questions for selecting the correct lubricant grade for a given brand and product are:

1. What is the minimum acceptable viscosity for a given bearing?
2. What is the optimum viscosity for the bearing at operating temperature?
3. What is the viscosity of the current lubricant at the normalized bearing (machine) operating temperature?

Determining the minimum allowable viscosity to sustain element and race separation (EHD film formation) is a simple calculation, as follows:

V_min= 27,878 * RPM ^-0.7114  * Dm ^-0.52

Where:

V_min   = minimum allowable viscosity

RPM = shaft rotational speed

Dm    = bearing mean diameter

For example, assuming the bearings on a 254-frame-size motor are operating at 2400 RPM, and contain single row deep groove ball bearings with a bore diameter (ID) of 45 mm and an outer diameter (OD) of 85 mm, then the pitch diameter is 65 mm. The minimum allowable oil thickness for EHD film formation would be 12.505 centistokes at operating temperature.  The optimum operating viscosity will be three to five times this value, or 36 to 60 centistokes.

Once determined, this should be compared to the viscosity supplied by the selected lubricant.  Assuming the grease contains a 100 centistoke (ISO VG 100) oil, and the bearing is operating at 50°C, one can use a commonly available viscosity/temperature chart to determine the acceptability of the operating viscosity of the product in use.  Figure 2 illustrates this process.

Matching operating viscosity to bearing needs is the cornerstone of reliable lubrication.

As can be seen in the example, the suggested product would fulfill the optimum viscosity, delivering 60 centistokes at the stated temperature.  The product would function with a margin up to 65°C, and deliver the minimum allowable viscosity to 95°C. 

As long as the dynamic (operating) viscosity is above the minimum allowable viscosity, the use of EP agents is discouraged.  This example reflects why many electric motor lubricants are filled with wear resistance (AW) rather than seizure resistance (EP) agents and contain ISO 100 viscosity oils.

Viscosity selection for other bearing types and speeds follows this pattern.  The bearing’s maximum allowable operating speed and the limiting speed for grease lubrication (the point at which any given bearing should be oil lubricated) is determined by the bearing Pitch Line Velocity (PLV = mean bearing diameter times shaft speed = n*dM). 

Spherical and thrust bearings approaching a PLV of 150K, and ball and roller bearings approaching PVL values of 350K must be qualified for reliable operation with grease.

Choosing the Right NLGI Grade for Application Conditions

Grease stiffness influences grease performance in the bearing cavity.  The stiffer, or harder, the grease is, the less it will move within the housing once initial movement and settling have occurred.  There are nine grades of stiffness, as defined by the NLGI (National Lubricating Grease Institute).  The stiffness grades, and a parallel to a commonly recognized product, are shown in Figure 3.

Stiffness is a reflection of the amount of shear resistance that the grease presents to a weighted cone that is allowed to settle into a grease sample, as shown in Figure 4.  The rod that connects the cone to the instrument is also attached to a dial indicator at the top of the instrument. 

As the cone settles into the cup, the dial moves clockwise until movement stops. The number indicated by the dial is assigned to the grease as its stiffness value. The value correlates to the range of values on the NLGI Grade chart.

Assuming that the selection process has properly addressed the viscosity and additive type, selection of the grease grade (NLGI #1, #3, etc.) depends on bearing speed, temperature, vibration, shaft orientation, and application method.  Some general rules to follow:

1. Use #0, #1 for: Automatic systems with long distances, narrow feed lines, cold feed lines, significant number of 90°
2. Use #1 for: Outdoor single-point (low-pressure) applicators
3. Use #3 for: Vertical shaft axis applications.
4. Use #3 for: Very large bearings, high vibration conditions, very high-speed conditions, very high temperature conditions.
5. Use #2 for: Manual, battery powered, or air powered grease gun applications, moderate to low speeds, low vibration rates, and low heat load.

The majority of grease-fed components can be successfully serviced with #2 grade greases.   However, some circumstances warrant a change.  If the selected grease tends to show puddles of oil on the grease surface of unopened containers, then a step up in NLGI grade is appropriate.

If a bearing housing proves consistently difficult to purge, then consider moving to a softer grade.  If the bearing is subject to grease dilution or removal from frequent exposure to water, or wash down activities, consider a stiffer grade.

Calculating Initial Grease Fill and Replenishment Volumes

When an element bearing is first placed into service, the initial fill volume in the housing (if space permits) should be based on the volume needed to fill the base of the housing up to the bottom edge of an element sitting at the 6:00 position in the race.

If it is not feasible to observe the internal spaces in the housing, then a fill volume equal to 3X the replenishment volume of bearing for low-speed bearings, and 1X for high-speed bearings. In this instance, ultrasonic methods should be used to validate a proper oil film within 4 hours of initial operation.

Practical Formulas for Estimating Bearing Replenishment Volumes

There are two options for calculating the bearing net capacity and replenishment value. Schaeffler FAG bearings company provides an option to determine this as follows:

V = ((Pi/4) * W * (OD² – ID²) * 10^-9 – G/7800)*10⁶, where

V = volume in cubic centimeters,

OD = Bearing Outer Diameter, mm

ID = Bore Diameter, mm

W = Bearing Width, mm

G = Bearing weight, Kg

SKF bearing company provides an option to determine this volume as follows:

V = W * OD  * .005, where

V = volume in grams

OD = Bearing Outer Diameter, mm

W = Bearing Width, mm

From a practical perspective, the SKF approach offers greater flexibility in asset assessment when the exact bearing number (required for weight in Kg) is unavailable, making it the preferred method in LubeCoach calculations.

In addition to the grease introduced into the element spaces, enough grease should be placed into the housing to bring the grease level up to the lip of the outer race of the bearing.  When the excess from the initial fill is pushed away from the elements, it accumulates on the grease shelf at the race. It becomes a reservoir to continuously serve oil back to the raceway without crowding the elements.

A well-filled housing isn’t guesswork – it’s precision that feeds reliability.

The engineer/practitioner making these decisions has to know precisely which bearing by manufacturer number is in use to provide all the required values. Bearing manufacturer numbers are readily available at the time of initial installation and/or bearing replacement, so enough information is available for a correct initial fill.

Replenishment volumes: The bearing number details become fuzzy as repairs occur, CMMS systems are upgraded, and data is lost, and as the details from the original installation fade from memory. Therefore, it is necessary to have a more user-friendly approach to estimate replacement volumes for ‘in-situ’ applications.

One should consider both feed volume and feed interval since the two are interrelated. The formula shown in Figure 5 gives volumes in both grams (for metric dimensions) and ounces (for English dimensions) for three different interval ranges. 

Where actual bearing dimensions are not known, a close proximity to the actual suggested value could be estimated by using housing dimensions and factoring again by one-third {(D * B * .114) *.33}.

CAUTION: This provides only an approximation. For critical applications, the actual bearing make and model should be determined.

Excessive lubricant volume applied to bearings with labyrinth style seals and low pitch line velocity bearings (PLV ≤ 50,000 for ball and cylindrical roller, ≤ 30,000 for spherical and thrust roller) is not considered to be as problematic to the grease or bearing as it would be at higher speeds.

Excess grease dissipates readily, and any grease remaining in the working area has adequate transport time and space.  However, the same bearings with shields and plugged relief ports can accumulate grease residue. Over time, the residue can crowd the housing and cause churning and overheating. 

It is best to identify the precise bearing details for all relubrication volume and frequency calculations, and use the precise values to make well-defined decisions.

Grease Volume Guidelines for High-Speed Bearing Applications

The replacement volume for high pitch line velocity (PLV ≥ 330,000 for radial ball type; ≥ 150,000 for spherical roller and thrust type) element bearings requires thoughtful consideration due to shearing and heat produced by overfilling.  All bearings operating at high speeds benefit from more frequent but lower volume doses, emulating continuous replenishment that occurs with oil-lubricated elements.

At high speeds, it’s not about more grease – it’s about smaller, smarter doses.

For instance, the volume calculated for the short interval, Gq-Weekly, would ideally be uniformly distributed into the number of working hours for the period and applied accordingly. This technique would require automatic application, incorporating the use of timers and low-volume injectors or quality single-point lubricators.

Determining Optimal Grease Relubrication Intervals

The most dependable calculation for relubrication interval will be based on a combination of machine operating conditions and the expected grease service life for those conditions. Grease lifecycles can be predicted empirically.

Much like a bearing L₁₀ lifecycle value that indicates an operating interval for which 10% of a given bearing population would fail under identical operating conditions, the grease F_10Real value projects an operating interval for grease lifecycles and, consequently, relubrication intervals.

The F10 grease prediction model, as shown in Figure 6, is based on known grease degradation performance under test conditions, such as the FAG FE9 Tester (DIN 51821, Part 2), or similar test methods (SKF ROF Tester, DIN 51806).

The (theoretical) F_10Real formula for grease replenishment intervals, in hours, is shown in Figure 6.

Factor F₃ pertains to the actual operating temperature (given under T), and Factor F₄ pertains to the bearing load factor (given under P). Similar to the earlier comment about grease fill volumes, this approach works well when specific greases are being tested for specific applications during design considerations, but is difficult for the plant lubrication technician to apply to in-service components when the specific data points aren’t available.

When FE9 test data and F_10Real values for specific lubricant products are not available (it is typically not reported in OEM performance data), a modified approach can provide the reliability practitioner with a well-defined starting point. 

This empirically derived approach (formula shown in Figure 7) assumes applications where the actual load is a low percentage of net capacity, and where bearings are operating below the rated speed limits (Pitch line values are ≤ 300K for ball and roller type elements, ≤ 140K for spherical and thrust type elements).

In this approach, ‘K’ is the product of machine operating condition parameters, shown in Figure 8. The F₁₀ value is modified (hours to failure value is reduced) to allow equipment owners to factor in plant conditions.  Each of several factors becomes a judgment call, but with time and experience, results similar to the DIN 81825 calculation for net relubrication frequencies are achieved.

Where,

T_f = Time in hours between grease replenishment events

K = Product of environmental correction factors

N = Shaft speed

D = Bearing bore in millimeters

The correction factor, K, shown in Figure 8, allows the engineer to adjust frequencies based on machine operating and environmental considerations. The six provided conditions reflect practical issues that degrade bearing life and grease performance.

Figure 8 includes the correction factors for a 90 mm bore spherical roller bearing operating at 1200 rpm (PLV = 160,800) in direct exposure to rain and in a dusty environment, such as near an unpaved roadway and directly exposed to the weather. The calculated interval amounts to 18 days between relubrication events.

Multiple Bearing OEM Lubrication Guideline publications provide alternate quantitative approaches that are also valid and could be considered as a strong reference starting point.

Lubrication Practices for Single and Double Shielded Bearings

Key Differences Between Shields and Seals

Seals and shields perform similar functions in supporting an effective bearing lifecycle.  Shielded bearings may be used where no routine relubrication for the life of the machine is the design objective, but are typically used in housings where replenishment can be accomplished.  The key difference between sealed and shielded bearings is that shields are in contact with only one race, and seals contact both.

Grease Entry Paths in General Service Bearings

In general service bearing applications (pillow block, flange mount) grease may enter the raceway either from the face (axial feed) or from the outer perimeter of the bearing (radial feed).  Bearings are identified as radially fed in the OEM equipment catalog if they are serviced in this manner.

For instance, SKF identifies radial feed bearings with the W33 designation in the bearing number. Other bearing suppliers may use this or other nomenclature to differentiate between styles.  For bearings that are large enough that the housing is retained and only the element is replaced during a repair, the bearing will have an outer seal (lip or labyrinth type) at the outer periphery of the housing cavity.

Without a shield, gravity takes over – and so does premature grease failure.

It may or may not be equipped with a shield on the element itself.  The shield serves the function of metering grease and keeping contaminants out of the element area.  If the shield is missing from the element, then the grease slumps by gravity around the lower lip of the bearing and is drawn into the element gradually. This approach doesn’t prevent grease churning and premature loss of usefulness.

Configurations where the bearing and housing are replaced as a unit should contain shields on both faces.  Grease may enter axially or radially into the element pathway, and the shield in these instances is intended to vent pressure and prevent contamination entry.

Shield Orientation and Its Effect on Grease Flow

Electric motor bearing construction is highly user-specific.  If the user requests a shield or seal, then it can be supplied.  If the user doesn’t specify either, then it is the motor rebuilder’s or OEM’s prerogative to follow their advice. Unless the user specifically asks the question, he/she may not know.

Shield orientation is also user-driven.  The shield may face out or away from the windings. In these configurations, the annulus gap between the inner race and the shield performs a metering function, allowing grease to enter the raceway through the gap while in operation.

Shield direction shapes grease flow – and determines what stays cool and clean.

The grease also provides a baffle to prevent churning and heating of the grease away from the movement of the elements. It may also be configured with the shield facing toward the windings.  In these instances, the shield is thought to minimize the risk that the grease will enter the windings.

In both configurations, the gap between the lip of the shield and the inner face of the bearing ring is sufficiently open that fresh, viable grease is drawn into the raceway easily. The shield and gap can be seen in Figures 9 and 10.  Different installation arrangements can be seen in Figure 11.

Figure 10 provides a cross-sectional view of the element and races, and illustrates the gap in more detail.  The annulus is between 125 and 375 microns (0.005” and 0.015”). The shield also provides restraint of bulk contaminant flow into the raceway, but does not eliminate contamination problems.

Given that the dynamic element to race clearances ranges between 0.5 and 1.5 microns, it is clear that particulates that can corrupt the dynamic oil film can readily pass into the race area.

Installation Considerations for Shielded Bearings

Figure 11 (below) demonstrates accepted mounting techniques for shielded bearings in electric motor housings.  (Original Graphic Ref., Heinz Bloch, “Practical Lubrication for Industrial Facilities”). Single shield bearings may be installed such that the shield is facing the grease supply, or is on the opposite side of the bearing receiving grease supply.

When installed facing the flow of grease, the shield can behave as a baffle to limit the flow of grease, if the grease volume is not overpowering, and minimize the risk of churning.  Unfortunately, if grease is supplied under too much force (high pressure or volume), the shield may collapse into the raceway and compromise the bearing.  It is important to know which configuration exists, if possible, before proceeding with the lubrication event. 

There is no single position taken by bearing manufacturers for the use of shields and seals (single or double shield configurations).  Machine manufacturers select seals and shields when contamination from the environment is expected. Shields are also prevalent on electric motor applications. 

The shield is beneficial to prevent grease churning in the housing, but does not prevent the movement of the grease toward the center of the motor. The motor owner should be aware of the options provided by the builder and should publish and provide technical specifications according to what is believed to be best for the production site.

Best Practices for Initial Bearing Grease Fills

The initial fill for a single shielded bearing should conform to the advice provided above under open face bearings.  OEMs do not differentiate between fill and replenishment practices based on the bearing component or seal configuration. 

The quantity of grease to be placed into the bearing at the time of installation is governed by the vacant space within the bearing.  The quantity of grease for the housing is not definable because a bearing can be fitted to multiple bearing housings.  Bearings are shipped with a quantity of grease that serves as both a corrosion inhibitor and an initial charge for operation.

Any addition of grease via hand-packing before mounting the bearing should be conducted under clean room conditions with dust-free/lint-free gloves.  Even slight handling of element bearings can induce corrosion.

As noted previously, when a bearing is placed into a housing, it is necessary to create a grease floor in the housing that is flush with the outer race lip at the bottom of the housing.  This will allow any new grease to slump to the area at the bottom of the shield/open face and provide a renewing reservoir. 

Guidelines for Relubricating Shielded Bearings

The volume for replenishment is determined by the formulas provided above. The advice is based on bearing size and speed, grease longevity, and operating conditions.  Technicians should be aware of the use of shielded bearings and whether the shield faces the grease flow or is on the opposite side of the bearing.

Shielded bearings should be lubricated while the bearing is running to prevent overpressurization of the seal and possible collapse into the bearing pathway.  Movement of the elements during lubrication will cause the grease to draw into the element pathway for maximum flushing and distribution effectiveness.

Greasing on the run keeps pressure down and distribution up.

Bearings should not be greased while idle if possible.  Where this is necessary, the equipment owner must determine the minimal acceptable amount of grease for the installation and its operating conditions, and restrain grease addition to this value only to avoid collapsing the shield.

Short of physical observation of the immediate area at the bearing (which is not possible without disassembly of the housing/machine), it is not possible to know the pathway that the grease follows once it is in the housing. 

Understanding and Maintaining Sealed-for-Life Bearings

Within the last few years, there has been a marked increase in the dependence on sealed for life bearings for a wide variety of commercial, residential, and even some industrial machines.  The concept ‘sealed for life’ reflects the design goal, not the expected operational period.  ‘Sealed for life’ is also not a guarantee of operational performance. Sealed for life bearing applications have grown from the traditional deep groove ball bearing to include all shapes, sizes, and design parameters.

Equipment manufacturers’ primary determining factor for whether to choose a seal (not to be replenished while in use), a shield, or neither is driven by machine lifecycle cost and duration requirements.  For typical components where sealed bearings are widely or singularly used, the component supplier has concluded that the likelihood of achieving the required lifecycle is better if the component is not relubricated.

Figure 12. Sealed Bearing Configuration

Sealed bearing lifecycles are greatly influenced by the in-use grease condition, which is itself influenced by the seal condition (leakage and contaminant exclusion). The significant improvements seen in both grease and seal materials have enabled machine manufacturers to design for and achieve longer lifecycles with sealed bearings in progressively more challenging conditions.

Favorable conditions for sealed bearings could include:

• Small bearing dimensions
• Low shaft rotational speeds
• Low shaft circumferential speeds
• Low loads
• Clean conditions (no moisture, no dust)
• Low heat
• Short expected lifecycles

As the relative load, surface contact speed, temperature, and contaminant load increase dependence on shielded or open face relubricatable bearings increases. Sealed bearings are not intended to be relubricated during the machine’s expected lifecycle.

However, shielded bearings are configured for and are expected to be replenished at some interval.  Elastomeric radial lip seals are designed primarily to retain the lubricant and are only marginally expected to prevent external contaminant ingression.

Seals are capable of containing both liquids and semi-solids, are capable of operating in bearing sumps varying from -60 to 200°C, can operate with peripheral speeds up to 20 m/s, and support pressures between 20 and 100 kPa (2.9 to 14.5 PSI).  Seal radial loading is determined by the types of elastomers used, the contact area of the seal on the race surface, internal pressure from the fluid, and spring tension.

Every turn of the shaft turns the seal into a precision fluid pump.

As the shaft turns, the movement of the shaft causes the seal to flex. This provides a subtle pumping motion that serves to push the fluid toward its reservoir area. The fluid creates a film barrier between 0.125 mm and 1.25 mm wide. Lip contact load is a key performance factor.

Contact load ranges between 0.05 and 0.12 N/mm (0.3 to 0.7 lb/in) of circumference. As the lip load (spring tension) increases, the surface temperature rises in relation to shaft speed. Since temperature is a prime cause of seal failure, lip loads should be as low as possible and still maintain a seal. Figure 12 provides a look at the key features of a lip seal.

Key Takeaways for Effective Grease Relubrication

Grease relubrication practices should be handled with care.  Precise grease volumes and carefully calculated intervals will help the reliability professional reduce outages, reduce costs, improve machine performance, and enjoy a less stressful career.   The formulas provided above are either directly or indirectly associated with bearing supplier recommendations.

The LubeCoach recommendations reflect the principles noted in the formulas provided. These may be programmed into a worksheet with minimal effort.  The LubeCoach is designed to offer insights without requiring complex spreadsheet construction. Learn more about LubeCoach Circular Bearing Lubrication Calculators.

References

Con GMBH, Bearing lubrication Calculation Worksheet, FAG Bearings, German Society of Tribology, others.

FAG Bearings Limited, Roller Bearing Lubrication Guide, Publication Number WL 81 115/4 EC/ED

LubCon USA, LubCon GMBH, Bearing Lubrication Calculation Worksheet,

FAG Roller Bearing Lubrication Guideline WL81115E.

Machinery Lubrication magazine

Web Reference X.X – Timken Bearing Company

Web Reference X.X – SKF Bearing Company. http://mapro.skf.com.

Snyder, D.R “Sealed-for-Life Bearings: To Relubricate or Not?” Tribology and Lubrication Technology, December 2004. Pages 33 to 40.

Booser, R.E., Tribology Data Handbook, Chapter 14, Dynamic Seals.  CRC Press

Hodowanec, M.M., “Evaluation of Anti-Friction Bearing Lubrication Methods on Motor Life Cycle Cost”. Siemens Industry and Automation Incorporated. 0-7803-4785-4/98.  IEEE. 

All machines with moving parts have bearings of some type. The bearings may be as simple as flat surfaces working against other flat surfaces, such as the slideway in a machine tool, or they may have sophisticated geometries like a ball screw. Plain and element bearings supporting rotating shafts are found in nearly every machine type you might imagine.

Machine designers use sophisticated tools and techniques to create element and plain bearings that provide a specific function for the machine within which they are found.

This article provides reliability engineers and managers with simple but dependable guidelines for selecting lubricants with the correct chemical and viscometric qualities necessary for long-term reliable operation.

Different Bearing Types and Their Roles in Machine Reliability

Element bearings could be categorized by the function they are designed to provide. Assuming that the shaft’s axis is parallel to the ground, some bearings offer support for shafts with only radial (up and clown directional) load, while others provide support for both radial and axial (side-to-side directional) load.

Figure 1 shows the types and shapes of five common element bearings.

Roller bearings and deep groove ball bearings have elements shaped to support a load that is primarily in one direction perpendicular to the axis of the shaft.

Comparing the shape of the inner and outer rings (races) for the deep groove ball bearings to that of the thrust ball bearings, one can see from the difference in curvature of the race contact area around the ball (element) that the thrust ball type of bearing should be capable of with­ standing more axial force than the deep groove bearing.

Figure 2 shows the orientation of the force relative to the shape of the race in a radial thrust bearing. All bearings are designed by the designer to accommodate a given type (direction) and amount of thrust.

The OEM is responsible for installing the bearing into the machine in the proper orientation. In some instances the machine designer may choose to specify two thrust ball bearings with their respective thrust orientation turned opposite to one another to support a shaft with a load that moves back and forth.

The machine builder may select bearings designed to accommodate force in both directions for machines that operate with a significant amount of directional force along one or more shafts.

An increase in element surface area increases the load potential for the element bearing.

Cylindrical and spherical roller bearings are designed to support shafts with both radial and axial (directional) forces. Again, comparing the differences in the shapes of the elements and the races, one can see how the shape of the element conforms to the shape of the race, accommodating thrust from one or both directions.

One may also observe a large difference in the amount of contact surface areas between the races and elements of the deep groove ball bearing and the thrust and roller bearings. An increase in element surface area increases the load potential for the element bearing.

How Oil Films Protect and Extend Bearing Life

The type of oil film produced by mechanical components in dynamic interaction is dictated by the kind of surface interaction that the components experience.

Element bearings exhibit rolling contact characteristics and are characterized as forming and operating in EHD film conditions. EHD films are exceedingly thin, ranging between one-half and one-and-one-half microns thick. To put this into perspective, there are 25.4 microns in 1/1,000th of an inch.

Figure 3 provides an array of commonly recognized items categorized by their respective micron dimension. The dimensions of the oil film thicknesses representative of the EHD film are on par with the dimensions of a bacteria.

Despite the thinness of the EHD film condition, a properly established oil firm demonstrates remarkable durability when the lubricant is maintained in a healthy, clean, dry state.

The dynamic thickness of the EHD film is influenced by many design parameters, including:

1. Bearing material hardness
2. Material pliability
3. Dynamic loading
4. Dynamic temperature
5. Contact surface area
6. The lubricant pressure viscosity response (pressure viscosity coefficient)
7. The initial oil viscosity
8. Other parameters

A properly established oil film demonstrates remarkable durability when the lubricant is maintained in a healthy, clean, dry state.

In the selection process, the reliability engineer is keenly interested in ensuring that the selected lubricant meets the minimum acceptable operating limit to achieve an EHD film condition. The reliability engineer can do so by systematically following a few key principles and establishing an acceptable operating viscosity.

How to Select the Optimal Viscosity for Element Bearings

The most critical characteristic to establish is the lubricant’s viscosity at operating temperature. Viscosity changes with temperature and pressure. As temperature increases, viscosity decreases, and viscosity increases as pressure increases. These factors are interdependent.

The most critical characteristic to establish is the lubricant’s viscosity at operating temperature.

The pressure viscosity relationship depends on the type of raw materials used to construct the lubricant. For any given lubricant selection, the reliability engineer cannot change this characteristic, so we will focus on selecting the correct oil thickness regardless of the type of lubricant.

The central questions for selecting the correct lubricant grade for a given brand and product type are:

• What will the lubricant’s viscosity be at the normalized machine operating temperature?
• What are the allowable, minimum, and optimum viscosities for a given element bearing regardless of operating temperature?

The first question begs for knowledge of the machine’s operating state. Machine speed, load, process temperatures, oil viscosity, and frictional conditions at the element contact area influence temperature. If the machine is already in operation, then the answer may be evident from machine observation and measurement. If not, the reliability engineer must consult with the OEM and production personnel and collect sufficient information to project a safe answer.

For this exercise, assume that the temperature is known; we’ll use a figure of 154°F (70°C). We will also assume the shaft speed is 2,000 RPM, and the bearing has been properly selected for the application.

An exact number can be produced if every incremental de­ tail is known (speeds, loads, forces, material compositions and strengths, VP responses, etc.). As most plant circumstances afford only estimates of these details, this article provides a model that can be followed by plant personnel to appropriately answer questions without the requirement for a full set of exact details and a computer-aided design program.

Step 1

Locate a viscosity selection reference chart for element bearings. Fortunately, most bearing manufacturers provide suitable tables and charts in their lubrication reference guidebooks. Figure 4 is provided by FAG Bearings and is appropriate for this task¹.

Step 2

Use the following formula to estimate bearing pitch diameter, d111, where:

D_m = (OD + ID)/2
OD = Bearing Outer Diameter
ID = Bearing Bore

Assuming you wish to lubricate the bearings in a 254-frame-size motor containing bearings with a bore diameter (ID) of 45 mm and an outer diameter (OD) of 85 mm, the pitch diameter is 65 mm, locate this value on the chart’s x-axis (bottom of the chart), and plot a vertical line from this point to the top of the chart.

This line is referenced on the chart as item I.

Step 3

Determine shaft rotation speed (noted above as 2,000 RPM). Locate the diagonal line labeled with this value on the chart.

Step 4

Using a chart similar to the one in Figure 4, locate the intersection of the pitch diameter and shaft speed lines.

Step 5

Draw a line from this intersecting point to the left side of the chart, to the y-axis, to read the mini­ mum allowable viscosity in centistokes (mm2/sec).

Following these instructions, these points coincide on the y-axis at approximately 12 centistokes. This value represents the bearing manufacturer’s projected minimum operating viscosity or the required oil thickness at the normal machine operating temperature. It is advisable to try to provide three to four times this value as a target operating viscosity.

The practitioner must still determine which of the available grade options will deliver this result.

Step 6

Determine the correct starting viscosity (always measured at 40°C), as noted above. After observing the following steps, the practitioner may use Figure 5 to determine the viscosity starting point (viscosity value at 40°C)2.

Step 6 (a)

Determine the target viscosity (three times the required viscosity= 12 cSt * 3 = 36 cSt). Locate this viscosity value on the y-axis. Plot a line parallel to the x-axis (left to right) from this point.

Step 6 (b)

Locate the machine operating temperature on the x-axis. From this point, plot a line parallel to the y-axis (bottom to top).

Step 6(c)

Note where the two lines intersect. If the value is not at a normal ISO code specification, select the viscosity grade representing the next highest category. This chart represents paraffinic mineral oils with a viscosity index of around 100.

The black arrows in Figure 5 represent the minimum recommended operating viscosity parameters, and the red lines provide parameters to meet the preferred operating viscosity. A lubricant with a viscosity grade above ISO 100 and below ISO 150 would be appropriate.

Given that it is an electric motor bearing on a small frame-size motor that is nearly always grease lubricated, one should look for grease constructed with a viscosity grade at or slightly above 100 centistokes.

Choosing the Right Additives for Bearing Lubricants

The minimum allowable viscosity estimated for the conditions is expected to maintain a ‘fat’ (EHD) oil film in an element bearing. EHD conditions provide for complete separation of interfacing surfaces, but the separation ranges from a paltry 0.5 to 1.5 microns for ball and roller-type bearings.

Within this range (one-time minimum allowable limit), manufacturers suggest the use of rust and oxidation-fortified (R&O) mineral oils and greases containing these types of fortified oils.

Some bearing manufacturers and recognized authorities propose that wear-resistant (AW) and seizure-resistant (EP) additives should be incorporated to protect surfaces³ if the film ratio falls below the minimum allowable level.

It is possible to estimate whether a given bearing in a given set of conditions requires an EP-fortified oil or grease through a film thickness ratio K, or Kappa factor. This is the ratio of the proposed viscosity (at operating temperature) divided by the bearing manufacturers’ required minimum viscosity (at operating temperature).

A ratio of 3 is optimum, so a value of three times the allowable minimum was recommended during Step 6(a). Figure 6 shows a viscosity ratio range for which EP additives are highly recommended.

Choosing the correct oil viscosity can significantly impact bearing life and overall machine reliability.

A manufacturer’s general-purpose (GP) greases commonly have viscosities between 100 cSt and 220 cSt, even though most element-bearing applications carry minimum requirements in the 12 to 22 cSt range.

For very slow-moving and heavily loaded element bearings, it is appropriate to select even higher-viscosity oils and greases and incorporate solid-film agents for enhanced protection against shock loading and loss of EHD condition. Remember that thicker oils and grease consistencies tend to churn, generate heat, and consume energy, particularly in moderate to high-speed applications.

Element bearings are manufactured in a variety of sizes and configurations. Ball bearings have lower contact areas than thrust bearings, but bearings with higher contact areas can support greater loads. Element bearings have definable minimum allowable viscosity limits.

A reliability engineer may use a relatively simple approach to verify that the correct viscosities have been selected. Viscosities should be optimized to a level at least three times greater than the allowable minimum. Bearings that operate with viscosities below the recommended mini­ mum limit should incorporate wear and seizure-resistant additives (AW/EP).

References

1. FAG Roller Bearing Lubrication Guideline WL81115E.
2. SKF Corp. Bearing Maintenance and Installation Guide, p. 29. February 1992.
3. Moller, Boor. Lubricants in Operation, p. 116.

Have you ever wondered how a launched-from-scratch vibration program can require investment ranging into the mid-six figures, pull the most talented and skilled repairmen, and disrupt other condition-based agendas? I used to wonder. The answer boils down to the most crucial message in MBA programs worldwide: Cash is king.

Companies selling vibration analysis tools don’t compete with other companies, giving the tools away as a technique to get into some other supply relationship. They have to compete to earn the business, meaning they have to demonstrate value.

In the lubrication provision world, the value of oil analysis is trodden underfoot when it is strategically given away to entice a user to commit to a new supply arrangement. This is the nature of the business and isn’t evil. This approach meets a significant market interest and price-based competition for the lubricant supply arrangement.

Wishing this dynamic wasn’t so won’t make it go away. Those trying to sell oil analysis as a tool must agree that the best way to overcome “free” services is to demonstrate superior value for “purchased” services.

I contend that this is more about knowing the customer’s needs, the tool’s capability, the lab’s capacity to understand what the data means (and report accordingly), and financial analysis techniques than having the test slate delivered by a different laboratory.

The economic value proposition for oil analysis or any other condition monitoring technique is much greater than its simple cash flow value.

Many managers cover the cost of the expense by minimizing another cost elsewhere. That is conventional thinking. The same thinking prevents companies from optimizing their preventive maintenance task lists because doing so requires some initial investment. It is penny-wise and dollar-foolish.

Managers who are seriously intent on applying modern maintenance concepts, tools, and techniques to preserve machine health are aware of the benefit that oil analysis provides in terms of its long-term view into machine health. Belief alone, though, isn’t enough.

Some numerical form of justification is expected. In the following paragraphs, I’ll address three perspectives on how one might justify implementing or markedly improving an oil analysis program, beginning with a quick tally of the costs associated with setting up a program.

The Economics of Machine Health Monitoring

The tactical process starts with sample collection, and the secret to success is location, location, location! Drain port and drop-tube samples from sumps are helpful in looking into oil health, but oil health measurement is on the low end of the value proposition scale.

The lubricant soup will be largely homogenous from one side of the sump to the other. Contamination and wear debris, however, are not. To achieve consistency, sample collection requires a few key constraints, including:

Properly Staged Sample Collection Port

A sample collection port is a device permanently mounted into the machine and enables fluid to be extracted from the same ideal (one hopes) location each time a sample is drawn. This is particularly important for effective wear debris and contamination measurement since these two parts of oil analysis can deliver highly misleading differences in readings depending on where the sample is pulled.

Depending on materials and construction, sample ports range from $20 to $300. Assume an average of $150 for a one-time charge installed. To account for the long-term cost of maintaining the ports, expect to replace them every 1-3 years. This would be an aggressive replacement schedule. Nonetheless, bad things happen, so you should plan for the future.

Properly Devised Sample Procedures

Repeatability begins with the sample port. If installed in the correct location, repeatability is achieved easily enough. The next chore is to document the method, task an individual to collect samples and place the routine in the maintenance-scheduling program.

Sample collection documentation costs should run less than $100 per machine to hire a consultant to put it together. Much less if it is written internally.

Properly Selected Test Slate and Laboratory

Machine criticality, environmental conditions, the strictness of the alarm set, and the type of components under surveillance drive the test slate selection. High-criticality sumps should include ample testing to clearly define contamination and lubricant degradation conditions beyond routine particle count, FTIR, and crackle testing.

Laboratory test slates run from as little as $10 to as much as $60 for a routine sample. In this instance, cheaper doesn’t mean anything. Quality differences exist between labs to the extent that price shopping is nearly meaningless without some reasonable evaluation of the labs’ quality practices.

In-plant labor cost per sample represents around $23.63 to collect, label, package, and ship the sample (.5 hours x $35 x 1.35 = $23.63). This cost also should be factored into the net cost.

To be safe, assume a $35 median per sample lab price and $23.63 per sample collection cost. This should allow the site to maintain flexibility in selecting from a range of test methods for primary and secondary testing.

Properly Selected Test Interval

The sample interval should be determined after consideration of the same parameters, as noted for the test slate and lab selection. High-criticality machines operating in highly stressful environments with narrow alarm limits should be screened on very short (roughly weekly) intervals and lab-tested following any finding. This will drive the frequency toward monthly to quarterly for most machines. Low-critically machines may warrant analysis to determine oil change requirements, if nothing else.

Assume a quarterly routine at the minimum for critical sumps and an annual routine for non-critical sumps. In simple terms, with a combination of critical and non-critical machines requiring 400 samples per year over three years, we have something like this, as shown in the chart below:

Every company has slight differences. One must be sure to account for all of the discrete charges.

Following a typical criticality distribution where a quarter of a site’s machines are rated critical, a company with 100 critical machines would have a net population approaching 400 machines. Even though it wouldn’t be considered a large site, this is a slight increase in expense, rounding up to $2,650 per month.

Justifying The Plan

There are a couple of approaches to justify this effort. Short of having a database full of mechanical component replacement costs (which would simplify matters), here are four solid options.

Option 1 – Cash flow increase. In this view, the increase in expenses is covered by a decrease in other costs. Back to the sample size, assuming the 100 critical machines average 25 gallons of oil per machine and the fully burdened cost of the oil/lubricant is $24 per gallon, the price per sump change is $600 ($8 per gallon times 3.0 for the cost associated with purchasing, shipping, storage, planning, work-order generation, lubricant swap-out labor, waste oil handling, and disposal expense). The analysis cost is covered if one could avoid changing out just five machines per quarter or 20 machines per year.

Option 2 – Repair avoidance. If plant management is thinking critically and honestly, it would have to admit that the prospect of avoiding a mechanical repair each month is worth $2,650 in direct costs. One major save per 100 machines per year would cover the cost of program implementation. This seemingly is self-evident, but one must still evaluate based on facts.

There are many case studies on this topic in electronic and paper formats. In each instance, the scale of cost reductions enormously outweighed the cost of sampling and analysis. Anytime production losses are included, the cost-savings ratio is lopsided. Here are a few examples of overwhelming savings from standard production processes.

CASE STUDY 1

Company: DaimlerChrysler Stamping Plant, Warren, Mich.1

Problem 1: Sheared stud for a 1,000-ton Hamilton Press.

Problem 2: Cracked rocker arm for another 1,000-ton Hamilton Press.

Impact: Repairs cycle reduced to three weeks and 24 hours, respectively, vs. several months.

Oil analysis benefit: Wear debris analysis.

Accrued savings from avoidance: more than $1 million in repairs and production losses.

CASE STUDY 2

Company: Rompetrol Petromidia (refinery), Romania.2

Problem: Hydrogen compressor failure due to degasification performance loss.

Impact: Partial production losses during repair.

Accrued savings from avoidance in Euros: 2.94 million from unit production losses.

Oil analysis benefit: Gas contamination analysis.

Accrued savings from avoidance in Euros: 105,600 from repair avoidance.

Company: Mobil Oil (improvement case study).

Problem: Hydraulic mining shovel—premature hydraulic pump failures.

Maintenance cycle: Four failures in the first 27 months of operation.

Impact: $24,000 in repairs, $30,000 in production losses for each event.

Oil analysis benefit: Contamination and degradation monitoring and control.

Accrued savings from avoidance: $99,000 per year annual savings.

Option 3 – Productive capacity improvement. Reducing maintenance costs or avoiding a maintenance debacle isn’t the best reason to adopt an oil analysis or any other condition assessment program. Reducing the unit cost of production by increasing productive capacity means much more to plant profitability than incremental cost control.

A company’s cost of goods sold equals the total cost divided by units produced. Many things, some of which are uncontrollable, impact the numerator. Raw materials and energy are the primary components of material cost, and both are beyond the purchasing department’s control.

Given the escalating nature of both cost categories, increasing production is the best chance to move from the high-cost producer to the middle- or low-cost category.

 Efforts such as condition monitoring and control programs, which increase productive capacity without new capital investment, are highly desirable.

For example, the Rio Tinto Boron operations operate Terex haul trucks. During two months, the operation experienced unexpected failures on four Detroit Diesel 16V4000 engines. The rebuild cost is high for these large (2,000 +/- bhp) engines. The equipment owner evaluated the circumstances to avoid future failures.

Still, during discussions over tactics to prevent catastrophic failure, the team became convinced there was enough information in the oil and filter element analysis data to enable a rebuild cycle extension from 750,000 gallons of fuel (the OEM’s projected rebuild point) to 1 million gallons.

Given that these four engines were consuming fuel at an average rate of 36 gallons per hour, the extension would allow for an additional 6,950 hours (for each engine) of increased productive capacity from the initial capital expense.

Healthy skepticism was replaced with confidence as decisions were made to overhaul based on data, machine components were examined, and wear rates were confirmed. The group accomplished its expectations, but more importantly, the group expanded capacity without new (meaningful) capital expense.

These case studies affirm the point that oil analysis value can be demonstrated in several ways, including:

• Reduced machine capital-cost requirement per unit of work accomplished.
• Reduced average annual repair cost (through increased years of operation).
• Increased productive capacity for capital investment.
• Improved return on capital from value-enhancing company activity.
• Reduced direct expenses.

Option 4 – Financial analysis and modeling. An amalgam of the previous three concepts, this option is last in the discussion for a couple of reasons. Financial modeling is expected to be wholly objective; it presents the most potent argument to either adopt or reject the implementation of the technology, and it is difficult to do well because hard data is required.

Plenty of data can be found, but actual component lifecycle and cost data are sometimes difficult to locate. If not available in the computerized maintenance program, the next best place to look is the purchase record (file cabinet or computer record). Component replacement numbers, intervals between replacement, cost, and type are all relevant to the discussion.

Once the program implementation cost and improvement targets are determined, the commonly used financial models for value calculation work well enough. Return on Investment, Internal Rate of Return, and Net Present Value are valid.

In simple terms, each provides the projected savings less the projected cost and then discounts the long-term value of savings according to the cost of money during the evaluation period. Each gives an indication of whether it makes sense to proceed or not.

WearCheck South Africa presents one effective value calculation model. In his article, John Evans spells out how one can estimate an investment’s long-term value, arrives at a conservative 7.6:1 ratio for value received from an investment, and projects further that 10:1 is achievable.

Engineers at Ontario Power Generation published another value calculation model that shows a $136,000 avoidance savings. In this instance, the standing analysis program detected a problem on a small but critical pump. Detection and early action enabled management to avoid catastrophe and make repairs at substantially lower costs than would likely have been incurred if the program didn’t exist.

In the review, the weighted cost of a likely failure is estimated and presented as the savings accrued by avoiding a failure through testing. The analysis was extended to all similar pumps, which hadn’t been in the sample routine because of the small sump size. The authors did a thorough job of incorporating likely production cost risk into their estimates.

Value from an oil analysis program can be demonstrated in several ways, including (1.) cash flow improvement, (2.) failure avoidance, (3.) productive capacity improvement, and (4.) detailed assessment and financial modeling (which may include details from each of these three options).

The first step is to establish what is to be measured and estimate the cost to initiate the program. Some faith is warranted in oil-based condition monitoring techniques based on their historical strength. In simple terms, savings between 7 and 10 to 1 is achievable. The savings and production improvement value can be incredible if careful analysis is conducted.

Lubricant management could mean different things to different people within a facility. The maintenance planner or lube crew supervisor may view lubricant management as the process that assures all the machines scheduled for level checks, replenishment, and oil changes are serviced promptly.

The condition control technician may view this as sample collection for analysis and long-term planning. Each would be correct. This article addresses another aspect of reliability-centered lubrication: sump condition control for static sumps.

Non-Circulating Oil Sumps

A non-circulating or static sump is one where the lubricant remains with the components. The lubricant certainly moves around the components under protection.

In this instance, the static sump is one where the lubricant remains with the sump during operation, in contrast to the dynamic sump, where the lubricant drains or is pumped out of the fixture holding the components and is later returned.

A non-circulating or static sump is one where the lubricant remains with the components.

Static sumps for industrial machines are simple enclosures surrounding moving components. Equipment owners typically do not specify standards for seals, filters, heat limits, moisture control, sump volumes, or port dimensions and locations when bidding for simple machines with small sumps.

Consequently, simple assemblies like gear drives and bearing enclosures tend to be exposed to the environment through open vent ports and shaft seals. Machines with complex designs or operational parameters tend to incorporate forced circulation and supply in the design details and suffer less from incomplete design.

It is common to have high criticality rankings assigned to static sumps. It is common for these sumps to build up particularly high contamination loads. Unless effort is applied to controlling contaminant exposure, the associated components will have shortened lifecycles.

Controlling Lubricant Health

Much research suggests that many common wear problems are associated with overall lubricant condition and cleanliness. Oil- and grease-lubricated machines that operate with continuous environmental challenges and without the benefit of sump health controls experience short lifecycles and high repair costs.

Contamination control may be the single largest area for improvements from the implementation of precision lubrication practices.

Contaminants Reviewed

Industrial sites are ripe with contamination sources. The most common problems come from the air we breathe—moisture, particulate, heat, and the air itself.

Temperature changes occurring with normal ambient temperature differences or with normal operating cycles cause the machine to breathe. Although the movement is slight, contaminants from the air settle into the oil and remain until forcibly removed or drained from the sump.

The resident contaminant load can become significant through daily thermal cycles over an extended period. Unfortunately, because the failure modes are slow, it is difficult to see the damage caused by most contaminants until well past an appropriate time to act.

Let’s look at these sources more closely.

Moisture

Water contamination is the fuel that propels oil and machine destruction. Moisture accelerates wear through corrosion from direct contact with surfaces and chemical changes in the oil (particularly for AW and EP oils), increasing the risk of film collapsing under load. Condensation can form on the underside of tank lids, create rust, and thereby add to solid contaminant loads. Moisture also promotes vaporous cavitation and destruction of pump surfaces.

Particulate

Particles promote micropitting, fatigue, and three-body wear in proportion to their concentration in the oil. The solid particle sizes that impose the greatest threat to machine surfaces—small enough to get between the surfaces and bridge the oil film gap—are well below that which can be seen without a microscope.

Additionally, particles become more challenging to crush as their size decreases. Particles that are one to three microns in size are particularly tough and particularly destructive to machine surfaces.

Figures 1 and 2 depict the impact of contaminants on machine surfaces, denoted by whether they are particulate from machine wear (Figure 1) or atmospheric dust (Figure 2). Atmospheric dust can change the machine component’s surface profile if the particle’s hardness exceeds the component steel’s.

Silica-laden atmospheric dust can have a greater hardness rating than many machine steels. When dust particles fracture to a size small enough to enter the dynamic clearances (± 2 microns) at component contact interfaces, these hard, tough particles can cause jagged indentions in the surface profiles.

Wear debris particles existing at the higher particle counts mean higher wear rates—for all types of lubricated components. As wear increases, the catalytic effect of iron and copper debris accelerates chemical reactions and increases the rate of aging.

Air

Air provides oxygen, the other fuel that promotes chemical reactions and drives aging. About 10% of the volume of a container of oil is dissolved air. This is a natural state tolerated in formulation decisions but problematic in higher percentages.

Air entrainment or saturation can occur in static systems when the level is too high or too low when the lubricant is contaminated by water and process chemicals, or when there is a consequence of lost air removal additives.

Heat

Excess heat makes all of the previously noted problems bigger. The Arrhenius rate rule in organic chemistry shows that chemical reaction rates double with each 10°C temperature increase. Following that logic, the aging process increases as sump temperatures increase, doubling with each 10°C increase.

Heat is also added from surface friction, cavitation, and shear stress on the oil film as it thickens under pressure.

Preventing Contamination

With small sumps, prevention is much easier than removal. Prevention of contaminant ingression for pumps, small drives, bearing housings, and other low-volume sumps revolves around exclusion at the shaft seal points vent ports and cleaning the lubricant handling and top-up activities.

Vent Port Improvements

OEM-provided vent filters are typically not designed to arrest airborne contaminants. Vent covers are constructed from metal mesh. Even a 200-mesh screen, considered high quality, is porous, limiting particles that are 75 microns and greater. Covered screens may slow ingression from blowing wind and rain but not extensively.

Upgrades to vent ports are simple and low-cost. Vents should be upgraded to desiccant vent filters where machines operate near high humidity (70% relative humidity or greater).

The dominant suppliers provide models that incorporate high-quality (≥ 5-micron target size) media at the point of air entrance to increase the value of a desiccant element purchase.

Low-humidity applications would benefit from retrofitting to either desiccant or non-desiccant type elements. Still, the reliability engineer should be conscious of selecting an element that provides a dramatic improvement from the status quo.

Automotive oil filter elements target relatively large particles (β 35 = 90) and are not the best choice for production machines’ oil filtration. However, these elements ported to allow bi-directional air movement provide adequate capture effectiveness for low-particle velocity airflow.

It is a long-standing failure of machine design strategies to place open pipes or screens at vent port locations. The relative cost to close this point of intrusion could run as high as a couple hundred dollars per machine for the initial installation (including labor) and another hundred dollars per year for replacements if high-quality desiccant elements are used. The benefit of extended component and lubricant lifecycles can easily outweigh the cost.

Shaft Seal Improvements

Shaft seal points represent likely points for solid and moisture contaminant ingression. Figure 4 depicts a typical lip seal configuration. Lip seals have a contact fit with the shaft and, by design, are pressed against the shaft during operation.

The subtle movement of the seal from normal radial contact with the shaft causes the seal to flex slightly to perform a slight pumping motion. Lip seals are intended primarily to hold in the lubricant.

Seal longevity is directly influenced by heat, solid contaminants at the shaft-to-seal interface, and chemical attack due to normal lubricant leaching effects. If operating in climate-controlled conditions, such as a clean room condition required for the manufacture of computer chips, the simple lip seal may function for several thousand hours.

Sumps operating within high contaminant areas can experience loss of seal integrity in a couple of hundred hours.

Bearing isolators significantly reduce the risk of moisture or airborne contamination ingression across the shaft. Bearing isolators maintain a tight fit with the housing and the shaft and only experience rubbing contact between the stator and rotor. This allows for better lubricant sealing and better contaminant prevention.

Lubricant Handling and Top-Up Activities:

Routine lubricant handling practices are an easy third choice for improving lubrication management practices. Lubricants shipped in bulk from the blend plant to a local vendor and then repackaged or sent in a bulk truck to the local customers are subject to tremendous variability in cleanliness quality.

Vessels, including pails, kegs, drums, totes, and bulk trucks, are universally expected to be “clean enough” for end-use, but they are not for many modern manufacturing systems.

The major brands recognize the potential for corruption of the lubricant by the container and have developed rigorous practices for evaluating and condemning questionable containers.

But is that enough?

As it turns out, even following this practice, a high percentage of finished lubricants arrive at the plant site in an unacceptably dirty state for high-criticality machines. This does not suggest that the lubricant pumped into the auger-type trash compactor is too contaminated for safe use.

However, the lubricant intended for the plastic injection molding hydraulic system with pressure-compensated variable volume piston pumps and servo controls operating at 3300 PSI should be serviced before it goes into use.

Preconditioning lubricants before use is simple and relatively inexpensive. Several years ago, world-class manufacturers moved in this direction through simple side-stream filter systems employing high-efficiency, low-particle size media.

Figure 5 illustrates the concept of prefiltering the lubricant as it is being placed into the machine sump. High-capture efficiency elements (βx = 100; = 99%) collect nearly all the targeted particle sizes as the particles enter the element.

Theoretically, some high-efficiency elements remove all but .01% of the particles at and larger than the target particle size. This is immensely beneficial to the machine receiving the lubricant.

Following initial fill conditioning, the same system can be used to treat the oil in the machine’s sump while the machine is running. Figure 6 illustrates using the same filter system for long-term improvement of fluid operating conditions.

The same type of device can and should be used to control water. The same approach can control moisture, although specialized vacuum distillation systems are more effective than water-removal element inserts.

Side stream filtration should be scheduled as a routine PM practice for all sumps that have (1.) high-criticality rankings, (2.) a high potential repair charge, (3.) large sump capacity, or (4.) contain components that are sensitive to microscopic contaminants or moisture.

Proactive sump management protects both component and lubricant, extending expected lifecycles. Common contaminants that degrade the lubricant include atmospheric air, moisture, dust, and heat. Vent breathers help prevent much of the contamination from the air.

Replacing lip seals with bearing isolators helps limit ingression across the shaft to housing interfaces. Prefiltration of lubricant is necessary for high-criticality machines. Side-stream filtration should also be used systematically as a machine PM to improve fluid conditions and protect machine health.

Companies enhance workforce efficiency and performance through various strategies. The most significant labor group is the production sector. Managers, where possible, have integrated operators into systematic, structured, and occasionally complex pre-shift equipment inspections to assess if the machinery is primed for production. This practice is prevalent in specific production settings due to the unique interaction between the operator and the equipment.

The production of additional components is particularly suited to this method. This includes using machines for tire assembly before curing, gear machining, or metal frame stamping for incorporation into parts for completed products.

Industries with continuous processes, such as oil refining, cement and paper production, and chemical manufacturing, operate non-stop, ideally without a definite beginning and end point throughout a shift, day, or month. These manufacturing procedures have had limited success with operator-centric maintenance.

As leadership continues to seek methods to boost productivity, there will likely be an increased focus on operator-centric maintenance and lubrication tasks. Here are a few reasons why it’s beneficial to involve operators in machine maintenance:

1. Economic constraints compel manufacturers to operate with extreme efficiency.
2. The retirement of skilled workers (the boomer generation began retiring in 2012).
3. More experienced, driven, and skilled labor is needed to replace the retiring workforce.
4. Logical distribution of work.

Operator-Based Care

In both piece and continuous production processes, it’s crucial to thoroughly consider operator-based maintenance, including fundamental tasks such as machine lubrication checks. This concept isn’t novel. As a supplier service technician in the mid-1980s, I noticed several clients attempting to implement operator-based lubrication maintenance.

However, in most cases, the program was rushed into operation, leading to operators needing help with oil cans and grease guns, declining machine reliability, and, ultimately, abandoning the initiative.

In several instances, I queried department managers about why the program failed at their site. A common thread among these organizations was the need for clearly defined responsibilities and accountability. The expectations were vague, resulting in weak accountability.

This issue persists in the present day. Without clear definition and accountability, the quality of lubrication practices depends on the operators’ understanding of machine requirements and their good intentions. If the workers are motivated and skilled, reliable results can be expected. However, if this is not the case, the outcomes will likely be subpar.

The following are critical factors for the success of operator-based maintenance:

• Clearly defined program expectations
• Clearly defined tasks suitable for operators
• A simple, reliable, automated scheduling plan
• A solid commitment to maintaining accountability for task completion

While operators can and should complete specific tasks, they should not be responsible for all aspects of machine lubrication.

This article delves into the potential of operator-based lubrication practices.

Protect the Gap

The thickness of the oil film for element bearings and components with rolling interaction typically varies from half to one and a half millionths of a meter. The oil film is slightly thicker for journal bearings and components with sliding interaction, ranging from three to ten-millionths of a meter.

These films are susceptible to various disturbances, known as failure modes. Experts in engineering and tribology have identified numerous failure modes that recur persistently. The primary culprits include:

• Contaminated reservoirs (dust, water, machine wear debris, air, heat, other lubricants).
• The use of inappropriate lubricant (wrong viscosity or additive type).
• Incorrect reservoir volume (excessive in greased bearings, insufficient in oil reservoirs).

These factors pose significant risks to operational machine reservoirs and should ideally be eliminated. This raises a question about our continuous operational requirements:

Have we inadvertently incorporated failure into our procedures? Suppose maintenance and engineering managers are conscious of the recurring threats to the microscopic film, understand how routine activities can generate these threats, and agree that removing these defects is best. Why haven’t procedures been developed to prevent these threats?

Here are some essential but crucial daily requirements for successful operator participation in lubrication practices:

1. Ensure the machine reservoir has the necessary amount of oil or grease.
2. Confirm the correct product type for the application.
3. Prevent contamination.
4. Monitor and report any abnormalities.

These requirements are straightforward, simple, and easily recordable. In theory, vital components can endure for decades instead of just months or years if these conditions are met. However, the damaging consequences of not meeting these requirements are well established.

Establishing a reliability-focused and operator-driven lubrication practice isn’t complex, but it is meticulous.

Program design should manage as many details as possible with minimal human intervention. This involves:

• Intentional planning.
• Clear definition of machine care and program practice goals.
• Providing operators with the necessary training and tools.
• Utilizing available technological (hardware, software) tools for implementation and management.
• Management support is shown by consistently holding workers accountable.
• Choosing high-quality brands and securing local supplier service support.

Define the Program

The following features can identify an effective lubrication strategy based on operator involvement:

Well-articulated program aims and objectives, along with a system for accountability.

These aims should be in harmony with existing reliability enhancement targets, and the objectives should further these aims. Potential aims could encompass:

• Enhancing machine uptime and output via improved machine dependability.
• Decreasing direct expenses linked to maintenance labor.
• Lowering direct costs related to machine part replacement.
• Establishing lubrication methods that align with plant reliability goals.

Starting a program without total commitment is not advisable. Without complete acceptance and dedication from production management to the short- and long-term needs, the operator-based maintenance initiative will likely fail due to neglect.

A clear-cut accountability plan to back the aims is recommended. Production and shift operator management should be entirely committed to ensuring operator adherence, irrespective of any resistance.

Well-defined machine care and program practice goals.

These goals should focus on the tasks and specifics of the overarching program and specific machine needs. High-level program management goals could include:

• Optimizing lubrication tasks and frequencies based on machine dependability requirements (derived from standardized engineering practices).
• Achieving 100% first-time completion of all scheduled run-time activities.
• Limiting repeat notices for corrective action requests to a maximum of 10%.
• Conducting training and testing-based verification every six months.
• Implementing fully automated record management.

Once the strategic direction is provided (as suggested by the objectives), the reliability engineer and development team can devise the tactical steps required to realize the plan.

The tactical requirements supporting these include:

Optimization of lubrication tasks and frequencies should be tailored to the specific reliability needs of each machine.

• Establish or create a hierarchy based on the significance of each machine.
• A matrix encompassing lubrication, inspection, and condition-control needs and frequencies should be built, grounded on the criticality evaluation. This matrix should ensure that every machine is covered according to its level of importance.
• Standard operating procedures (SOPs) for each task type should be formulated based on the criticality evaluation and the matrix of necessary activities. These SOPs should be integrated into the required frequencies. The expectations for each machine should be clearly defined, leaving no room for uncertainty.
• All tasks and frequencies should be assembled and planned using a route-based program.

The goal is to achieve a 100% initial completion rate for all scheduled activities.

• Each route should be designed to have a manageable workload, ensuring that it can be completed each time it is scheduled.
• The production management team should emphasize the importance of promptly completing the route after it has been assigned.

The aim is to limit the repetition of corrective action request notices to a maximum of 10%.

• Operators should inform management about any changes in the operational state of the machine.
• These notices should be evaluated by the planning team and either scheduled for action or rejected with a valid reason.
• The inspection process should be carried out promptly.

The objective is to achieve a 100% success rate in training and testing-based verification every six months.

1. Operators should receive training that matches their expected level of responsibility.
2. The training should be specific to each task, covering all aspects of the tasks to be performed.
3. Initial training should be completed before tasks are assigned, which should be repeated every six months.
4. Wherever possible, training should be hands-on.

Providing operators with the necessary training and resources for their duties.

The essential tools needed are straightforward and cost-effective:

• Containers for oil handling that can be cleaned and sealed.
• Grease guns that come with volume meters.
• Devices for transferring/loading oil from one container to another.
• Transparent labeling for each machine indicating the needed lubricant.
• Containers for waste oil disposal (if oil changes are incorporated into the task list).

Utilizing the existing technological (hardware, software) resources for execution and administration.

Operators should not be burdened with unnecessary, lengthy manual documentation processes to prove the completion of the scheduled tasks. A fully automated record management system can be chosen from trustworthy suppliers, including quality evaluation modules on some existing CMMS packages.

The record management system should offer:

• Efficient handling of a large number of recurring tasks.
• Sequential task organization (lists, routes) displaying all necessary tasks, schedules, and procedures.
• Capability to attach supplementary documents (photos, sketches, diagrams, etc.) for a comprehensive depiction of each task would be beneficial.
• A method for operator feedback about each task, including the ability for:

1. 1. Indicating completion by time, date, and operator.
   2. Indicating reasons for non-completion.
   3. Indicating capture and reuse of operator observations.
   4. Indicating operator-suggested maintenance activities.
   5. Monitoring each task against required completion intervals.
   6. Tracking each suggested maintenance activity for completion.

Management should anticipate at least three years of focus from a committed technical resource to guarantee a complete culture shift. It should not tolerate hastily written notes from vaguely defined routes.

The importance of managerial support is underscored by the need to enforce employee responsibility consistently.

The absence of leadership and implementation can hinder the alteration of human behaviors. The most significant threat to the enduring success of this responsibility transition, and ultimately to the long-term enhancement of plant productivity and machine dependability, lies in the shift management’s role in reinforcing the discipline to accomplish all planned tasks.

Shift operators will develop a sense of ownership towards the program that reflects the attitudes of middle and senior management. If top management does not show an active interest in the daily and weekly fulfillment of tasks and ensure they are done according to the established quality plan, the tasks may eventually be neglected.

There have been cases where programs are ceremonially initiated by plant or senior production management actually taking up the task of cleaning, inspecting, and lubricating machines (i.e., leading by example). It can be advantageous if this ceremonial approach aligns with the plant culture. However, if it doesn’t, it could be detrimental.

Choosing a quality brand and local supplier service support.

The choice of a lubricant vendor is equally vital for an operator-based plan as it would be for a mechanic or lubrication technician-based plan. Ensuring a clean, dry, and chemically correct lubricant supply is crucial and is probably the easiest part of the plan to execute.

It’s a frequent mistake to gauge the success of a plant lubrication program based on the reputation of the brand or supplier’s quality rather than the actual outcomes of the program.

While vendor and product quality are undoubtedly important, even the highest quality products won’t yield satisfactory results if they are mishandled during application.

The focus on operation-based machine care, particularly lubrication care, has been a topic of interest for senior management for many years. Yet, it is not commonly implemented in continuous process plants. A well-thought-out plan and a steadfast commitment to consistently carry out scheduled practices can deliver the expected quality.

A well-devised plan will inherently be reliability-centered and machine-specific, including clear, achievable, measurable goals and objectives. The plan starts with a detailed task development machine review, an assessment of material resources required for the tasks in the plan, and a suitable time allocation for completion.

A planning and tracking system is built around the tasks to facilitate regular tracking of multiple instances of multiple tasks/events with minimal reliance on manual record keeping.

Operator training is designed around machine-specific tasks, routes, and tools for delivery. Besides the evident support from management’s resource allocation to the development of the practices, management should visibly and vocally demonstrate their support by holding employees accountable for completing their work.

For years, machine reliability practitioners have heard that outdoor lubricant storage is something to avoid, if possible. There are several reasons for this position, including:

• Risk of lubricant oxidation from prolonged exposure to heat from sunlight
• Risk of increased lubricant contamination
• Risk of container rusting and failure

Those reasons are all valid, but the risk of contaminant load is significant.

We’ve been told that, particularly during hot weather, lubricants can heat inside their steel containers, which increases internal pressures and risks air discharge and fumes.

And, during these hot periods, IF the hot container of oil experiences rapid contraction from routine rain-shower activities, then the same container experiences a vacuum condition that may be strong enough to draw any moisture settling around openings right into the reservoir.

This advice has been met with resistance from time to time. After all, these drums are SEALED! The steel openings are fitted with tight (sometimes too tight) plugs and bung fixtures.

Water isn’t getting through that! Evidence that demands a verdict!

This video paints a picture worth the proverbial thousand words:

While the openings seem like they should be airtight, they are not. Further, the amount of pressure, and then vacuum, that can occur with the heating and shrinking of the volume of lubricant in the container is substantial.

Beyond the increase or decrease of the vapor phase at the top of the drum (tote, keg, or pail), the lubricant inside the container expands and contracts substantially with heating and cooling.

The lubricant packagers know this and respond using a pre-planned chart that designates how much metered volume should be placed in the container of a given size based on the temperature of the lubricant during packaging.

For those products sold by the pound, instead of the ‘gallon,’ this isn’t needed. The weight doesn’t change as the temperature changes, but the space that the lubricant occupies undoubtedly does.

55 gallons of hot oil occupies a fair bit more space than 55 gallons of cold oil.

Left in direct sunlight, the liquid and gaseous phases expand, and at night, or following a shower, they contract, causing the drum to exhale and inhale around any possible pathway that might exist.

The air bubbles in the video demonstrate that the drum has no tight seal. Water will follow a vacuum into the oil and accelerate the corrupting process. Following multiple thermal cycles, it is possible to accumulate a fair volume of water in the drum. Nothing good happens after this process begins.

If your lubricants are staged outdoors, they are at risk of inducing vapor or liquid phase water. Options exist for ‘insta-storage’ bins made from steel shipping crates.

Please call AMRRI if you’d like to know more about options for proper lubricant storage. 615-771-6030

Thanks to Felipe da Silva Ramos and Gregory Mecomber for the videos and image of oil drum bungs.

Condition-based greasing is an old and desirable idea. It is the finesse approach to fulfilling grease-based bearing care when done with precision. Efficient. Effective. Reliability-Enhancing. The most desirable objective for grease-lubricated bearings.

It can be systematically and utterly destructive when done improperly (without precision).

Whether this mode of grease replacement inherently enhances or kills your machine’s longevity is related to the practices developed and followed at your site.

In this article we’ll explore the following:

• A review of condition-based greasing
• Challenges with modern data collection prescriptions
  • Data collection and quality issues
  • Cost and efficiency challenges related to determining true condition-based intervals
• A recommended technique for fulfilling the promise of condition-based greasing
• The benefits of condition-based greasing

What is Condition-based Greasing?

Condition-based grease application is a grease replenishment practice triggered by increased bearing decibel values, the first hint of dry bearing surfaces.

Graphic 1 represents a snapshot of the interaction between a race and an element. The surfaces are separated by a thin film of oil, which could come from grease or oil in a reservoir. For grease-based applications, we expect the oil to either bleed from or volatilize from the thickener with time and shear stress.

As this occurs, the available oil reservoir dissipates, the oil film gets thinner, and eventually, the high spots on the races and elements begin to bump and rub. When this occurs, these contact points create sound waves that are well beyond the sensitivity of human ears. We refer to this commercially as ‘ultrasound.’

Sharp points inside the red circle in Graphic 1 are called asperities. Machining and finishing form asperities on machine surfaces, including gear faces, cylinder faces, element bearings, and other parts. These asperities serve the purpose of preventing oil from being easily displaced from the load-contact point. However, it can cause problems if the oil film dissipates.

Ultrasound Detection for Condition-based Greasing

Ultrasound is created whenever asperities at machine surfaces collide. The sound waves emanate from the collisions in all directions.

The effect is similar to if you took a tuning fork designed to produce 35 kilohertz sound waves and pounded the tabletop vigorously. You would only hear the sound if you had a device that would convert the high-frequency sound waves into a frequency range acceptable for human perception.

To describe the wave created by contact energy, please consider Graphic 2, a steel ball dropped onto a steel plate. The moment of contact creates a compression wave that transmits at an exceptionally high speed through the solid plate.

This wave is measured and represented in decibels, a standard unit for measuring sound, as a measure of intensity. The sound waves are very short and occur at, and above 30-kilohertz frequencies, so we need help ‘hearing’ the contact event.

Graphic 3 represents what follows the initial contact. The weight of the ball causes displacement of the plate. The plate flexes up and down following displacement. The upward and downward movement of the plate can be depicted in a waveform that could be measured and reported in various engineering units—measurement of displacement energy central to what occurs during vibration analysis.

The upward and downward energy waves occur at a much lower speed than the waves passing through a solid steel surface. Each form wave energy can be accurately measured with the proper tools.

Compression wave energy transmits very well through solid steel surfaces, so if we could find a way to accurately register that the moment of contact has occurred, then we could use the feedback to alter the risk of any further contact occurring by replacing the oil film intended to keep surfaces apart.

ALL lubrication practices aim to create conditions where that oil film is perpetually healthy, and the components can permanently float on the oil film.

If our underlying decisions are accurate, then, regardless of speed, load, and bearing surface area, we can make the machine parts’ float’ on a film of oil that is thinner than the width of a red blood cell.

Suppose we accurately calculate the oil thickness required for a machine surface to ‘float’ the load-bearing components operating at a given temperature, speed, and load. In that case, those asperities never or rarely have a chance to bump into one another.

The objective of the calculations is to identify precisely which lubricant is needed for the given surface area, surface speed, unit load, and operating temperature relative to the dimensions (height) of the asperities, how often it should be provided, and how much is required to keep surfaces apart.

If we have an accurate plan, we achieve a ‘Lambda’ value (aka specific film thickness) of one (1) or greater. Graphic 4 represents the factors for asperity dimensions (r) and oil film thickness (h).

When the oil film thickness (h) in microns is twice the asperity height (r), then we achieve a Lambda value of one (1), or one times the required oil film thickness. Graphic 1 (above) shows the result of having a Lambda of 1 or greater. Graphic 5 shows the result of a Lambda value of less than one.

Any influence on the ‘steady state’ supply of the right lubricant, in the right volume and time interval, can cause the film to dissipate and produce the effect shown in Graphic 5.

Recognizing this undesirable state, we set about to replenish the lubricant through a ‘just right’ daily care and feeding plan to ensure that the correct volume is always present at the element, race, gear face, or any other interacting machine parts.

We love the notion of condition-based greasing because it promises us the means to hear when the surfaces are bumping and rubbing and provides just enough to stop this failure root cause before damage to the bearing can occur.

That is a very appealing prospect.

Conducting the calculations to make proper decisions, including the timing of grease replacement, is relatively easy, but someone must take the time to fulfill this need.

With this information as a backdrop, let’s consider what it takes to accurately measure this faint energy level when it begins to occur.

Data Collection and Data Quality Practical Challenges

As with oil analysis condition-based machine health measurement, sample collection quality is at the top of the list of Key Success Factors. There is potential for substantial signal intensity (attenuation) loss for various reasons. This condition monitoring technique will only fulfill expectations if the data collection method produces highly repeatable, high-quality signal recognition.

The two predominant challenges with compression wave collection are:

1. Single attenuation through reflectance and refraction
2. Quality of the sensor configuration in use

Both represent a potentially severe dissipation of signal strength during measurement. Let’s take a shallow look at each of these.

Signal Attenuation

Attenuation means the loss of signal strength as measured in decibels (dB). Low signal strength during readings can occur for a variety of common reasons, including:

• capability (sensitivity) of the sensor and instrument
• repeatability in the data collection process
• differences between the type of metal at the data collection point versus the signal generation point (aluminum zerk fittings against steel pipe nipple)
• very low shaft speed (<30 rpm)
• large bearing housing mass
• sensor positioning that causes reflection and refraction

While all of these are common, the last can produce a substantial damping impact on dB readings for a few good reasons.

With each mechanical interface, the sound waves reflect and refract, causing substantial losses to occur to signal strength.

If the sensor is placed around the top of the housing, such as on the zerk fitting at the top of the housing (the 12:00 position location for Graphic 4), as is a common recommendation for instrument providers) then the signal must pass across multiple interfaces, including those of dissimilar metals.

With each new interface (inner race to shaft at the 6:00 position, inner race to shaft at the 12:00 position, outer race to housing, housing to pipe nipple, pipe nipple to zerk, etc.), a part of the signal bounces back (reflection) and a part bounces off in another direction (refraction).

Aside from all the signal bending and bouncing, most asperity contact occurs at the center of the load zone where the oil is under maximum displacement pressure. For optimum signal detection, the sensor should be placed at the center of the load zone either axially (at the 5:00 to 7:00 positions under the shaft) or radially (perpendicular to the shaft on a plane equal to the lowest element position in rotation), or as close to the center as possible.

Poor signal placement forces the technician to make full-confidence judgment calls without clearly understanding surface conditions. In practical terms, the technician doesn’t hear asperity contacts because the signal is being ‘lost’ due to data collection methods.

Consequently, the technician only supplies grease once bearing distress is excessive. The technician inadequately lubricates the bearing by putting an insufficient amount of grease into the housing, appearing adequate due to the diminished signal.

Quality of the Sensor Configuration

There are two points of sensor configuration to consider.

The sensor’s sensitivity (can it detect a 35 kHz signal) and the mode of sensor placement wherever it may be placed.

Companies promoting compression wave detection are addressing the sensor frequency quality issues well enough to be satisfied that if all other conditions are met, the technology delivers on the promise of advanced oil film health measurement.

The second aspect of Sensor Configuration involves the precise method of attaching the sensor to the machine. As demonstrated by Graphic 7, the nature of the contact mode is essential for maximum dB detection at high-frequency ranges. Options one, two, and three are popular modes for placing sensors on surfaces because they are straightforward, but they are not very helpful.

Options four, five, and six require management and technicians to put substantial effort into sensor placement to avoid any energy leakage.

The most promoted approach employs stinger probes or 2-pole and flat magnets due to their relative ease of use and low setup cost (no gluing or drill/tap/thread work). However, coupled with the Signal Attenuation issues already discussed, a poor sample collection technique can compromise the detection of whatever signal might be present.

Proper technique is most crucial at frequencies above 10 kilohertz. As noted previously, compression waves travel at 30 kilohertz.

Per Wilcoxon Corporation, the ‘best practice’ for high-frequency energy capture is to use adhesive with mounting pads (lower cost approach), adhesive with permanently mounted sensors, or a stud-mounted sensor.

If options such as 4, 5, or 6 are not possible, management should abandon the notion of strictly condition-based greasing. If the asset carries a top criticality level, then this upgrade is well worth the relatively low cost of the effort.

Challenges Associated with ‘True’ Condition-Based Greasing Practices: Timing of the Visits

There are three choices for setting the visit schedule to measure for a dB change that signals a need to replenish. To be clear, success with this technique means catching the ‘dry bearing’ conditions at the earliest possible stage and supplying just the quantity needed to re-float the surfaces.

The options are as follows:

1. True Condition-Based Approach – Measure every bearing daily until you have an interval.
2. False Condition-Based Approach – Pick an interval and incrementally adjust from there.
3. Calculate the ‘best fit’ interval and refine it to a condition-based approach by making adjustments until the best fit is determined.

Let’s look at the cost and duration to perform each of these as applied to electric motor lubrication practices. Instrument providers often prioritize this as a sales focus due to the challenging nature of proper motor lubrication.

For the sake of an apples-to-apples comparison between these three modes, let’s assume that the bearing manufacturer has told us that each motor requires replenishment at 244 days based on the conditions noted in Graphic 8.

At first glance, this is counter-intuitive because we are accustomed to lubricating motors on 6- and 12-month cycles. After all, that’s just what we’ve always done!

Assume the following:

1. There are 100 critical 75 HP motors, and you have configured measurement for the most technically viable data collection options.
2. We believe (from the calculation) that the best frequency is 128 days.
3. Each ‘visit’ to the motor bear will take 5 minutes.
4. The labor rate is $60.00 per hour, making each visit worth $5.00 in cost.

Scenario 1: Measure every day (the ‘True’ approach).

Cost:

• 244 * 5 minutes * $1.00 per minute = $1,200 per motor.
• $1,200 per motor * 100 motors = $120,000

Work hours required:

• 244 * 5 minutes each = 1,220 minutes per bearing.
• 1,220 minutes / 60 minutes per hour = 20.33 hours per motor.
• 33 hours * 100 motors = 2,033 expended work hours for the 100 motors

Scenario 1 requires a full work year from the technical trades to fulfill the promise of condition-based lubrication for only 100 hours.

Scenario 2: Use a repeating pattern to reduce cost and shorten the determining cycle

Measure bearings starting from some repeating pattern, and make adjustments until the ‘best fit’ is determined.

A repeating pattern could be anything you like. Since we have a ‘village lore’ based history of lubricating motors on month-increments (6 months, 12 months, etc..), we could start with what is already in place.

We will lubricate and adjust (extend) the interval with each interval until we identify the dry bearing condition. Knowing we’ve gone too far, we’ll take a fraction of the last adjustment and shorten the interval. For instance:

Lubricate the bearing, and then check six months later (condition-based lube check – visit 1). We find no grease is needed in our apples-to-apples comparison of the 244-day expectation. Lubricate again, and check in 12 months.

Visit 2: At 12 months (now 18 months into the investigation), we see that the interval is too long, so we lubricate again, deduct one-half of the LAST interval adjustment (6 months is shortened to a three-month adjustment to (12 – 3 = ) a new interval of 9 months.

Visit 3: We return at nine months and see that the bearing is dry again. (now 27 months into the investigation). We relubricate, cut the last ‘adjustment’ by half, and reset the new interval to (9 months less 1.5 months = ) 7.5 months, or 225 days.

Visit 4: We return at 225 days (now 25.5 months in) and see that the bearing does not yet need lubrication. We EXTEND the interval by ½ of the last adjustment (7.5 months plus 3/4 of a month = ) 8.25 months, and we find that the dB value has risen slightly, and it is time to lubricate based on condition.

In sum, using this method, it has taken 33.75 months to ‘find’ the suitable interval based on condition, and we have made four visits and expended ($5.00 per visit * 4 visits = ) $20.00 in labor for the motor. For 100 motors, we have spent (5 minutes per minute at $1.00 per minute * 100 motors = ) $2000.00 and taken three years (rounded) to make decisions about the 100 critical motors. Certainly a better outcome, but we didn’t take the purist approach with a strictly condition-based estimate.

Scenario 3: Calculate a ‘near ideal’ interval, and shorten the correction cycle.

This approach, like scenario 2, is NOT a true condition-based plan. Like scenario 2, we will pick a starting point and adjust as needed by small increments to extend or shorten the cycle to find the ‘best fit’ interval.

Unlike scenario 2, this approach will begin with standardized engineering practices. The LubeCoach software in Graphic 8, is based on DIN Standard 51825 (with slight modification for practitioner use) to calculate the interval best fit based on the bearing in its actual operating conditions.

The DIN standard was pioneered through the effort of a working committee of bearing manufacturers in the mid-1980s and is considered the best option available to make this type of determination.

The original DIN standard incorporates measures for the C/P Load factor (static to dynamic loading ratio – something we are not privy to with a machine that has been in operation for years) and ALSO a grease life factor (F10, hours, a value known by lubricant manufacturers, but is NOT published) as well. If you’d like to learn more about the variations, see these articles (PDF) on Optimizing Lubrication Effectiveness Part 1 and Part 2. 

Scenario 3 requires that the reliability engineer goes to the motor, records the shaft speed, bearing numbers, shaft orientation (horizontal or vertical), temperature, moisture load, particulate load, and vibration level, and plugs values to the appropriate locations in the calculator. The output, as shown in Graphic 8, provides a specific interval for service, as follows:

Visit 1: @ 244 days, measure dB value for replenishment requirement. If the bearing is dry, replenish and reduce the interval by 10%. If the dB values are still low (oil film is good), extend the interval by 10%.

Visit 2: At either 220 or 268 days, measure the dB value for the replenishment requirement and make another incremental adjustment based on 50% of the last adjustment value.

Visit 3: (now between 464 and 512 days in) Repeat step 2 and adjust similarly as needed. Experience suggests that two adjustments will enable the technician to achieve the desired ‘condition based’ regrease interval.

With this method, the site is in search mode for between 48 and 42 months and has an expenditure for field checks at $15.00 per bearing and $1,500 for the proposed lot of 100 motors.

Extrapolating Condition-Based Regrease Practices to the Entire Bearing Population

Even a small production site (150 to 200 assets) will have a large population of oil and grease-lubricated bearings operating at different speeds, loads, temperatures, and operating environments. The oil-lubricated bearing maintenance is simple: make sure the oil in the machine is the right type and at the right level.

The grease-lubricated bearings will create a morass of complicated scheduling and schedule monitoring based on the intervals that could be scattered between weekly to multiples of years based on the sizes, speeds, and other operating conditions.

It is possible to produce, execute, adjust, and eventually finalize a proper condition-based interval.

However, that doesn’t mean it is cost-effective or operationally efficient to do so. If/when the exercise from start to finish is measured in years and requires years of technicians’ time, and costs well above six figures even for a small production site, then true condition-based intervals (scenario 1) selection is not feasible.

Scenarios 2 and 3, which eventually identify the condition-based interval, are much more cost and time efficient, with scenario 3 producing the most efficiency.

Benefits of Condition-Based Greasing Practices

The core benefit of condition-based machine care of any sort is the opportunity to keep the asset operating in a productive state. Bearing replacements are disruptive and costly before you factor in the cost of lost production time. Lost production time triggers the worst negative consequence of parts replacement – the risk of losing customers due to missed shipments.

Condition-based, or modified condition based, regrease activities should be directed toward the most critical assets. Assuring that the proper lubricant is applied in the appropriate volume and at the right time is the first line of defense against machine repairs.

Refining condition-based greasing with a well-defined starting point enable the technicians to determine the optimum state without wasting time and money.

What are Base Oils?

Base oils are the starting material for producing lubricants, and their properties greatly influence the performance and characteristics of the finished lubricant. They are typically derived from crude oil but can also be made from synthetic or bio-based sources. The American Petroleum Institute classifies them into five base oil groups.

Base oils define the inherent properties of the finished product, including viscosity, stability/longevity, and load-bearing capacity (the ability to withstand extreme pressures).

For example, a lubricant made with a high-quality, highly refined base oil may have better thermal and oxidative stability than a lubricant made with a lower-quality base oil but NOT have the same degree of load-bearing capacity as a result of the molecular structure and purity.

As a result, the choice of base oil is an essential consideration in producing lubricants. Consequently, selection requires careful thinking and planning around the machine’s operating conditions to produce a finished product that serves the long-term performance interests of the machine owner.

Base Oil Categories

The three general categories of base oils are mineral, synthetic, and bio-based. Beyond these categories, there are well-defined and accepted technical categories that lubricant manufacturers use to select base oils.

Mineral

Mineral base oils are derived from crude oil and are the most commonly used type. They are relatively inexpensive and widely available but also have some limitations, such as a relatively low viscosity index and poor thermal stability.

Mineral base oils are classified according to their refining process and viscosity, such as paraffinic, naphthenic, or aromatic.

Synthetic

Synthetic base oils are man-made and can be tailored to have specific properties, such as a high viscosity index or superior thermal stability. They are typically more expensive than mineral, but they can improve machine performance in many applications.

Synthetic base oils are classified according to their chemical structure, such as PAOs (polyalpha olefin), PAGs (poly alkaline glycol), or esters (diester, polyol ester, phosphate ester, etc.).

Bio-based

Bio-based are derived from renewable sources like vegetable oils or animal fats. They may have similar properties to mineral base oils but are more biodegradable and environmentally friendly.

Bio-based base oils are typically classified according to their feedstock, such as vegetable oil-based or animal fat-based. Like synthetic base stocks, bio-based materials are considered entirely man-made (synthesized) and are expected to demand a higher price.

Advantages and Disadvantages

The advantages and disadvantages of each base oil type depend on the lubricant’s specific application and performance requirements. Mineral oils have the advantage of being widely available and less expensive, but they might have limited performance in particular applications.

Synthetics have the advantage of being tailored to have specific properties, but they may be less compatible with certain additives or seal materials.

Bio-based have the advantage of being environmentally friendly and biodegradable, but are more expensive (than mineral oils) and have somewhat limited availability.

The fundamental base oil properties important in producing lubricants include viscosity, viscosity index, pour point, flash point, and thermal stability. These properties determine how well it will maintain its flow characteristics at different temperatures, how well it will resist oxidation and breakdown, and how well it will protect against wear and friction.

The specific properties of each type will vary depending on its source and refining process.

Base Oil Production and Refining

The process of extracting base oils from crude oil involves several steps, including crude oil selection and preparation, distillation, and refining.

First, the crude oil is selected and prepared for refining by removing impurities such as water, sediment, and other contaminants. The crude oil is then heated and distilled to separate into different fractions based on their boiling point. The lighter fractions are used to make gasoline and other fuels, and the heavier fractions are used to make base oils.

The heavy fractions of crude oil used to make base oils are called lubricating oil stocks, and they typically have a high viscosity and a complex chemical structure. These lubricating oil stocks are then refined to produce finished base oils. The refining process may involve several steps, such as solvent refining, hydrocracking, or iso-dewaxing, to remove impurities, improve the chemical structure, and improve the performance properties of the base oil.

After refining, the base stocks are packaged and shipped to lubricant blenders (manufacturers), where base stocks are mixed with additive blends to produce finished lubricants.

The refining process and the additives used can vary depending on the type of base oil and the desired properties of the finished lubricant.

Base Oil Groups

A classification system from the American Petroleum Institute (API) categorizes lubricating oils according to their production process and performance characteristics. This rating system enables lubricant producers and users to communicate easily about the inherent performance differences that exist due to the makeup of each base oil category. There are five main groups, numbered from one to five.

Group I

Group I base oils are mineral oils derived from petroleum crude and prepared through solvent refining and hydrofinishing. They are the least refined option and contain the most significant degree of variability in the molecule (hydrocarbon) shapes and sizes.

Due to the variability, these base oils are prone to shorter lifecycles (due to the presence of benzene ring structures that are prone to decay). Still, they are also oddly capable enough of providing the highest load support (due to the presence of naphthene ring structures).

Also, due to the molecular variability, Grade I stocks have the broadest range of viscosities from which the blender can select to produce finished lubricants.

Accordingly, Group I oils represent a strange combination of potentially short lifecycles (durability) and superior load-bearing support. Because they are the least refined, they USED to be the least expensive.

With a market shift in production of the last 20 years to higher durability Group II and III stocks, the nature of supply and demand has created conditions where the Group I stocks will price at and above their hypothetically higher quality counterparts.

Group II

Group II are also mineral oil-based materials derived from crude oil. They are produced through a refining process known as hydrocracking, which involves breaking down the larger, more complex molecules (naphthene and benzene ring structures) into smaller, simpler, more uniform molecules. This process results in a purer base oil with improved durability characteristics compared to Group I. Group II are commonly used in the production of engine, hydraulic, turbine, compressor oils, and other lubricants for machines that benefit from a higher level of performance and purity.

They are also generally more expensive than group I. As the hydrocracker breaks molecules into smaller and more uniformly shaped molecules, the viscosity range shrinks toward the low to medium range.

Group III

Group III base oils are also mineral oil-based materials derived from crude oil. Group III materials are also produced through hydrocracking, similar to the method used to make group II oils.

However, group III undergo an additional step called hydro-isomerization, which further rearranges the molecules into an even more uniform and stable structure. This results in a purer base oil with even better durability and temperature response characteristics compared to Group I or Group II.

Group III oils are commonly used to produce lubricants operating under high temperatures where longevity is a particular interest, such as compressor and gas turbine oil, engine oils, and transmission fluids.

Group IV

Group IV are completely synthesized (man-made) oils that begin with an extract from petroleum crude: ethylene or C2H4. They are produced through a chemical process that involves the creation of new molecules rather than refining existing ones. This results in a molecule shaped like a branched paraffin, but it is too pure, uniform, and highly organized to be called a branched paraffin.

Group IV base oils are commonly used to produce high-performance lubricants, such as motor oils and transmission fluids. The specific name for Group 4 base stocks is PolyalphaOlefins. They are also referred to commercially as SHC, an abbreviation for Synthetic HydroCarbon.

Group V

Group V base oils include all that do not fit into any other groups. It is a catch-all category that encompasses a wide variety of base oils, including synthetic lubricants, bio-based oils, and any other type of oil that does not fall into one of the first four groups.

Group V can have a wide range of properties and performance characteristics, depending on their specific composition and production process. They are commonly used in various applications, from automotive to industrial lubricants. Like group IV, group V oils can be expensive, depending on the specific type of oil and its intended use.

Some other examples of group V, include esters, poly-glycols, silicone oils, perfluoropolyethers (PFPEs), and other specialty oils used in specific applications.

Base Oil Applications

Base oils are used as lubricants in many industries and applications, including automotive, aviation, industrial, and many others. Base stocks represent 90% to 99% of a finished industrial lubricant and 70% to 90% of finished automotive engine and transmission oils.

In the industrial sector, base oils are used as lubricants in various applications, such as gear oils, compressor and turbine oils, hydraulic fluids, and greases. They are chosen based on the equipment’s specific performance requirements and operating conditions, such as the temperature, load, and speed, to provide the necessary lubrication and protection.

In the automotive industry, which includes construction, rail, and mining machinery, base oils are used as lubricants in various applications, such as motor oil, transmission fluid, gear and hydraulic oils, and brake fluid.

They are chosen based on their performance characteristics, such as their viscosity, thermal stability, and wear protection, to provide the necessary lubrication and protection for the various components of a vehicle or machine.

In the aviation industry, base oils are used as lubricants in aircraft engines, hydraulic systems, and other applications. They are chosen for their ability to withstand the high and low temperatures, pressures, and loads encountered in aviation applications.

Base oils are also used as lubricants in many other applications, such as marine and agriculture.

Emerging and Specialized Applications

In addition to the traditional industries and applications, emerging and specialized applications are starting to use base oils or are developing new ones to meet their specific needs.

One emerging application is in the field of electric vehicles (EVs). As EVs become more popular, there is a growing need for lubricants that can meet the specific performance requirements and operating conditions of EV components, such as electric motors and battery systems.

This has led to the development of specialized base oils and lubricants for EVs, with improved thermal stability, low toxicity, and compatibility with EV components.

Another specialized application is in the field of medical devices. Medical devices, such as implantable and medical instruments, require lubricants that can meet strict requirements for biocompatibility, sterility, and performance.

These requirements call for specialized base oils and lubricants for medical applications, with improved biocompatibility and performance in sterilization processes.

The need for improved performance, biocompatibility, and environmental performance in various industries and applications drives base oil’s emerging and specialized applications.

The industry will evolve and innovate to meet the changing needs of its customers as new technologies and applications develop.

Physical Properties

Several physical properties are used to characterize base oils. Some of the most important physical properties include the following:

• Viscosity: A measure of a fluid’s resistance to flow. Oils with a higher viscosity will have a thicker consistency and flow more slowly than those with a lower viscosity.
• Viscosity index: A measure of the change in viscosity of a base oil with temperature. A base oil with a high viscosity index will have a relatively stable viscosity over a wide range of temperatures.

• Pour point: The lowest temperature at which a base oil will flow. Oils with a low pour point are preferred for cold weather conditions.
• Flash point: The temperature at which a base oil gives off sufficient vapor to ignite in the presence of an ignition source. Oils with a high flash point are less likely to ignite or cause a fire.
• Clarity: Refers to the transparency or clarity of the base oil when it is in a liquid state. A clear oil will be transparent and free of any suspended particles or impurities that could affect its performance.
• Volatility: Refers to the extent of fluid displaced (turns to vapor) when exposed to high temperatures. A base stock’s volatility is a crucial performance indicator for its usefulness in high-temperature applications like combustion engines.

Other physical properties include density, refractive index, and surface tension.

History of Base Oils

The use of oils as lubricants dates back to ancient times when people used animal fats and vegetable oils to reduce friction and wear in mechanical devices such as chariots and water mills. With the birth and growth of the industrial era, mineral oils have been extracted from crude oil and used as lubricants, providing improved performance and stability compared to animal-based oils.

The modern base oil industry began to develop in the early 20th century, with refining processes that could produce high-quality base oils from crude oil.

Over time, the technology has continued to evolve, with the development of synthetic and bio-based oils and new refining processes that can produce them with improved properties.

Today, the base oil industry is global, with companies producing base oils in many different countries and supplying them to lubricant manufacturers worldwide.

The industry is highly competitive, with companies constantly seeking ways to improve the quality and performance of their base oils and reduce the environmental impact of their production.

Here are some key milestones and innovations in the history of base oils:

• 1859: The first commercial oil well is drilled in Pennsylvania, USA, ushering in the era of petroleum-based lubricants.
• 1868: The first lubricating oil patent is granted in the USA for an oil made from sperm whale oil and tallow.
• 1869: The first lubricating oil refinery is built in Cleveland, Ohio, USA, to produce kerosene and lubricating oil from crude oil.
• 1902: The first hydrocracking process is developed, allowing for the production of high-quality base oils from crude oil.
• 1920s: The first solvent refining processes were developed, allowing for the production of highly refined base oils with improved properties.
• 1940s: Synthetic base oils are developed, including polyalphaolefins (PAOs) and polyalkylene glycols (PAGs).
• 1990s: Bio-based base oils are developed from renewable sources such as animal fats and vegetable oils.
• 2010s: New refining processes are developed to produce base oils with improved environmental performance, such as hydroisomerization and isodewaxing.

The importance of base oils in lubricant production and various industries cannot be overstated. They provide the foundation for lubricants, and the performance and their properties significantly affect the performance and characteristics of the finished lubricant.

As a result, the base oil industry is a critical part of the global economy. Continued evolution and innovation will play a vital role in developing new technologies and applications in many industries.

With all that maintenance personnel must do daily in their industrial, manufacturing, and mining environments, why should management task their engineering resources to invest time, energy, and money into a ‘Precision Lubrication’ work plan?

Because the industrial world floats on an oil film that is less than the thickness of a red blood cell, and if we don’t protect that film – we lose.

Daily lubrication care and feeding of machines is a reliability cornerstone.

If it can be done with utterly precise definition and deployment, mechanical machine repair work will decline. Precision Lubrication work practices will impact the pace and intensity of the industrial/manufacturing environment for the better.

The Indirect Impact: The most prominent reason to focus on improvements in this foundational plant practice is to improve plant capacity. MRO reductions may inspire the initiative; however, regardless of the size of any MRO savings, this value pales in comparison to the value accrued to the organization through dependable, repeatable capacity.

Dependable, repeatable capacity enables progress in multiple underlying aspects of enterprise management: reduced COGS, improved or sustained quality, improved safety performance, improved customer satisfaction, improved financial performance, improved value for stockholders, and improved job security for the persons involved in the enterprise.

The Direct Impact: Precision Machine lubrication also enhances the direct financial performance of the maintenance practice. Consider this: for every dollar spent on lubricant purchases, a capital-intensive manufacturing plant will also pay between $10 and 20 dollars on repairs of lubricated and their tangent components. The site will also spend $3-5 on labor for each dollar in lubricant purchases.

Analyze your budget, and you will find this relationship to exist.

To put this in another context, for each dollar the site spends on lubricants, it will spend, on average, another $20 to sustain the operation of lubricated components.

Two changes must occur to reduce MRO expenses, particularly those costs relating to machine repair.

• First, create a work plan that assures that the thin layer of oil can be sustained. 
• Second, make the oil film between the components cleaner. 

That’s it. Accomplish these two changes, and the MRO expense will decline.  Theoretically, it must decrease. Accomplishing these two changes is not easy, but it is certainly possible and is highly lucrative for the machine owner.

The Benefit of Wider, Cleaner Dynamic Oil Film Clearances

The impact of improvements in the selection, application, and maintenance of the lubricant to accomplish the two results (thicker, cleaner) can be immediately recognized through reduced costs in lubricant use, labor use, and parts replacement.

Each lubrication program assessment (Benchmark/Gap Analysis) to date has uncovered overwhelming cash flow and five–year return potential when the following program parameters are analyzed:

• Product consolidation and inventory reduction
• Product (lubricant) lifecycle extensions
• Product cleanliness management
• Lubricant application and replenishment rates
• Sampling and Analysis improvements – sample collection
• Sampling and Analysis improvements – test selection and alarm setting development
• Component rebuild reductions

The most significant financial impact, limiting production losses, is generally not included for various reasons. 

The Economic Driver – Reduced Cost of Operations

Because it is a ‘maintenance’ function, and maintenance is generally responsible for managing the cost of existing capacity rather than expanding capacity at a reduced unit cost, the likely driver will be reduced ongoing cost of machine care. 

Fortunately, the long-term improvement in cash flow from combined reductions in labor consumption, material consumption, machine parts consumption (machine repair), and lost production (due to scheduled and unscheduled downtime) represents a tremendous dividend for an arguably minuscule investment. 

Building Precision Lubrication

 Creating a precision lubrication work plan is not complex.  Calculus is complex.  This isn’t like doing calculus.  However, it is complicated due to the many variables that must be considered when building precision lubrication work plans. 

 AMRRI follows a systematic plan refined through 35 years of lubrication work plan development. This plan can be replicated by company personnel at the production site if they are willing to put in the effort. 

 The steps are as follows:

1. Create a floor plan that shows the location of all rotating assets.
2. Using the drawing, define an efficient and linear path between one machine to the next in the production area. Working with management and technicians, define the machine care sequence that represents the fewest possible steps from one machine to the next. This becomes the sequence for the operator-based care and/or the lubrication route.
3. Following this path/sequence, collect information about each lubricated component on each machine.
4. Log the machines and their respective components into a task management system.
5. Log the discreet component lubrication activities into the task management system.
6. Generate weekly machine care routines based on production area routes.
7. Track the completion (or lack of completion) of each task.
8. Generate performance reports based on what is getting done

 I’ll elaborate on each of these actions below.  Suppose the reliability or maintenance engineer is given the time to follow each of the steps noted below. In that case, that engineer can build and deploy a daily care plan that can completely change the nature of maintenance in their facility.  Let’s get started.

Step A: Creating a Floor Plan (aka Mapping)

The only constant that we can count on is change.  Change in the workforce has become a relentless challenge for industrial/manufacturing production and maintenance management.  This seems especially true for this particular role in the maintenance department. As new persons enter this role, regardless of whether they are an old-timer or newcomers, they should have access to a plan that shows the most efficient way to do the job. Defining that efficient plan begins with a high-level view of the production floor. 

To accomplish this, we use Excel to create a plot and populate that plot with tanks, stairwells, elevators, and of course, ALL of the operating machines.  As shown in the drawing below (Diagram 1), creating the structure to produce a floor plan rapidly is very simple in Excel.

A simple grid pattern with a scale for horizontal and vertical orientation, along with simple graphics representing common elements, can be quickly generated and replicated as needed.

Once the essential elements are available, the engineer will walk down the operating cell, making notes about the location and distance between relevant interests, and then transfer those notes to the excel worksheet.

Step B: Route Design

Once machines are plotted, it is possible to see an efficient pathway through the machines. Diagram 2 represents a floor plan with a suggested route pathway.  It is best to have maintenance and technician involved in plotting the route pathway so that the route reflects technician interests.

Step C: Collection of component-specific machine information.

After defining the route sequence, the persons collecting machine data return to the machines in the order established by the route sequence and locate every moving component in the drive train.  Some of these may not require lubrication but should be included to prescribe some level of inspection of those machine parts if possible.

Once the components are identified and categorized, the program builder will apply the well-established engineering principles available for the respective lubricated machine parts to define the parameters of the lubrication work plan.

For example, element bearings are defined through the following six steps and calculations.

Step 1

Determine if the bearing in its current operating state is suitable for grease or requires oil.  The bearing manufacturers suggest calculating the nDm value and comparing that value to the speed limit factors for the bearing.  If nDm is lower than the limiting factor, then grease-based care should be acceptable to deliver long life cycles. If nDm is above grease’s limiting factor, then oil should be used.

Step 2

Calculate the nDm.  It is shaft speed multiplied by the median diameter ((ID + OD) / 2).  Bearings have different speed limits based on bearing type and design for axial loading.  Diagram 3 represents generally accepted parameters for oil and grease speed limits.

Step 3

Determine the minimum allowable viscosity requirement for the bearing.  The formula provided for this is:

Dm = bearing median diameter, and was previously noted. RPM is shaft rotating speed in revolutions per minute. This formula is designed for double-roll spherical rolling bearings. Still, it is suitable for determining requirements for other bearing types, leaving just slightly higher viscosity requirements per bearing type than the actual formulas designated for ball, needle, and roller-type bearings.

Once we know the minimum viscosity limit, we can calculate the actual viscosity provided by the selected lubricant or plot that value on a chart. 

Step 4

Determine the viscosity at the component’s operating temperature.  Diagram 4 represents the viscosity changes with temperature for several VI 95 mineral oils.  The program builder provides an operating temperature for the bearing and plots that temperature against the viscosity of the lubricant in use (regardless of oil or grease-based replenishment) to determine what the operating viscosity actually is and, therefore whether that lubricant is an acceptable selection.  In the example, the operating temperature is 55°C, and the grease is manufactured using ISO 100 (100 cSt) mineral oil. Accordingly, the operating viscosity is 50 cSt. 

As long as the operating viscosity is above the calculated minimum, preferably between three and five times above the minimum, the lubricant selection is a good choice.  Outside of that range, it is worth examining more closely.

Step 5

Determine the proper volume per replenishment cycle. This does not apply to oil-lubricated machines since our objective with those is to maintain an identified oil level. Still, it is essential for grease-based machine care that we avoid overfilling the bearing cavity with each replenishment cycle. 

 Two formulas could be used for this, as proposed by either SKF or FAG bearing companies. The output for either is very similar, but the required information is much easier with the SKF formula, so we’ll look at this option.

 Per SKF, the bearing width multiplied by the axial width of the bearing multiplied by the imperial or metric constant value gives us the quantity of grease that the bearing cavity (space around the elements and between the rings) can hold.  Once that quantity is delivered, additional grease can be problematic. This is situational, related to the nature of the sealing method and the rotating speed.  Sometimes flushing profusely is the best call, but typically it is best to calculate the capacity and stop with that volume.

 The SKF bearing area highlighted in orange in Diagram 5 represents the area that should be filled with the calculated quantity. If the bearing is lubricated while in service, the elements will press the grease to the sides as it is being supplied, the elements and races will be ‘washed’ with fresh grease, and a reservoir will pile up adjacent to the sides at the bottom of the race.  

Step 6

The final step is determining how often the specified quantity should be applied.  This step is a bit more mathematical but is easily accomplished using excel.  Formula 2 below identifies a calculation that closely matches frequencies provided by DIN 51825 but without the problems associated with determining the static-to-dynamic load ratio (a machine design decision) OR the F₁₀ grease lifecycle value (a lubricant manufacturer value that is rarely published for public use).

Formula 2, as used by AMRRI, is as follows:

Where:

d = bearing bore in millimeters
n = shaft speed, revolutions per minute
K = product of the selected discount factors for the operating conditions

 Diagram 6 reviews the six operating conditions that should be reviewed and used as appropriate.

Once these values are all collected and calculations made, the program builder has an objectively planned, quantitatively defined lubrication service plan for the bearings. 

For low-speed bearings, since shaft RPM (denominator factor) so substantially influences the net interval, it is possible to see long service intervals.  To avoid excessively long intervals, once the value is determined, it should be pro-rated (along with grease volume) for some value at one year or less to ensure there are ‘eyes on’ the components at least once a year.

There are different but equally essential engineering principles (formulas) for gears, couplings, journal bearings, hydraulic elements, and other lubricated machine components that will not be addressed in this brief article. These principles and formulas are all in the public domain and can be found by searching vendor websites and periodicals.

The net effect of applying standardized engineering principles to the component reviews is the development of technically accurate, efficient, and practical work plans for each component.

Diagram 7 provides a limited example of what the output would look like for just a few assets.

Steps D and E: Deployment of machines and tasks into a Task Management Software

Having all the details organized in this manner for all tasks that support asset rotation makes it easy to populate machines, and their respective tasks, into a management system. CMMS programs traditionally do NOT provide data fields needed to house information related to sub-sub-sub machine elements.

Accordingly, while it may be a magnificent system for many other things, SAP (and other enterprise systems) is an inefficient tool to track tasks that should be scheduled and managed at the sub-sub-sub asset level.

Task management software is designed with extra levels of hierarchal structure to accommodate work planning at the level where the work is to be done. Further, task management systems can be used for many tasks beyond lubrication-related activities (fire extinguisher checks, safety system/equipment checks, food production safety documentation, etc.).

For machine lubrication purposes, scheduling and tracking each lubrication task in mass, by route, and then reporting completion records is an excellent benefit to site management.

Once populated and organized in the linear sequence, the system sets up for operation by route structure and sequence similar to what we see in the green box within Diagram 8.  Each task has a permanently assigned sequence number.

A properly engineered program will have tasks that will occur at many different intervals, as seen in the red box in Diagram 8.  In this small example, based on the stated intervals, it is evident that things will appear in the weekly schedule periodically, with very few tasks appearing each week that the schedule is generated.

However, whatever tasks are generated with the weekly schedule will all be organized in the same familiar sequence.

Diagram 9 shows what a typical work distribution would look like.  The sequence numbers create the order of output in the route, regardless of which of the 24 task items shows up with each work period.

Since each task is independently defined, each task is independently trackable. And, since pre-organized groups schedule each task, management can schedule thousands of tasks with a few keystrokes in a matter of minutes. 

With site lubrication details organized this way, and with each detail represented as a data field (rather than a text script), management will have the means to generate reports on any of the data fields used to build the plan, including work completion percentage, tasks skipped, completion dates for tasks, lubricants consumed, where lubricants of a specific type are used, etc.

The examples used in this paper are from LUBE-IT, the world’s most widely used lubrication management software. It is equipped with 60+ standardized reports and the means to make custom reports based on each customer’s KPI preferences.

The industrial world floats on an oil film that is less than the thickness of a red blood cell.  We have to get this right. 

Lubricant purchases represent one to three percent of the maintenance budget. Labor for machine lubrication is another three to five percent, including salaries and wages. The expense is a rounding error to the annual operations budget but impacts 35% of an industrial maintenance budget.

Suppose precision is applied to this element of industrial maintenance—the potential to improve productivity and reduce cost by avoiding machine repairs. Building a precise lubrication practice requires the application of well-established engineering principles. It can be completed by personnel at the site if they focus and are given time to fulfill the steps.

A well-executed Precision Lubrication work plan is foundational to turning a money-losing operation into a very competitive and financially healthy organization. 

If you understand the importance of keeping contaminants out of new industrial lubricants during storage, and you’ve worked to keep them clean, cool, and dry – great work! You are almost to the finish line and have one more task to get right before these oils begin doing their job.

Assuming the lubricant was delivered according to quality expectations and maintained in a clean state while in inventory, the remaining opportunity for corruption is when the oil is put into the machine sump. Topping off the machine is the last chance to harm the lubricant and the machine accidentally. Using a few simple precautions, you can eliminate this remaining threat.

High Volume Reservoirs

When topping high-volume reservoirs (10 gallons or more), equip the sump drain and fill ports with fluid quick-connectors to allow prefiltering with a filter cart during the oil transfer process. Precleaning the fittings before each use is simple and quick if you keep the connector covered with a rubber or metal cap while the machine is in normal run mode.

Ensure your filter elements have high dirt-holding capacity, low back-pressure limits, and at least β10 = 75 quality performance. The filtration system should be capable of filtering high-viscosity oils (up to ISO 680 is best) at a low flow rate (one to five gallons per minute).

Filter systems for larger bulk tanks (five drums or more) should have flow characteristics at five gallons per minute. High flow rates and high pressures can make some filter elements less effective.

Low Volume Reservoirs

When topping low-volume reservoirs (10 gallons or less), consider these guidelines:

1. Use a soft bristle brush to remove dust or dirt accumulated around the port plug.
2. If there is wet residue around the plug, use a clean, lint-free cloth to physically wipe clean the area around the port plug.
3. Loosen the plug and repeat Step 1 if you see any solid debris.